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Oyster
03-11-2017, 05:59 PM
Good evening gents. I apologize for the click bait like tittle but I didn't know any other way to word it. I recently bought a tida td-4a. It's a 10x24 lathe made in tiawain in the early 80s, like the Chinese made jet but heavier, and from what little is out there on the internet, a bit more rigid. It came with a Dorian tool post and the pictures will tell the story. While obviously not ideal, what is the opinion of the fine folks here as to how likely the tool post is to be ripped out of the compound, into the chuck, only to be launched into my pearly whites? I guess it's worth noting the base of the Dorian tool post currently in use fills the slot completely. https://uploads.tapatalk-cdn.com/20170311/6b741b0d664b00e9b15608378386557e.jpg

Cheers


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bob308
03-11-2017, 06:15 PM
if the tee nut fills the tee slot I would not worry about it.

Danl
03-11-2017, 06:16 PM
The lathe looks to be somewhat higher quality than some of today's units of similar size. I would not use that compound rest at all. If you have a mill I suppose you could shave those broken areas off all the way back to where they end and braze in some new pieces. Being OCD, I would probably also use some countersunk fasteners for insurance.

No way to see if you could find a replacement or something close enough to use?

Dan L

Toolguy
03-11-2017, 06:20 PM
Not good. The remaining lips at the top are too thin and can break off easily. I would repair by milling off the broken parts and replace with 1/4" thick steel strips on each side with 3 or 4 flathead socket cap screws, then mill the assembly flat with a face mill or end mill. There is plenty of meat for the screws and the repair will last as long as the lathe.

lakeside53
03-11-2017, 06:24 PM
Yep, fix it... many ways; I'd use Durabar (quality cast iron), mill off the entire top part and screw on another.

JoeLee
03-11-2017, 06:35 PM
I find it not likely that a tool post T-nut would be ripped out of the compound under normal use and the downward force against the post, but...
Looking at that compound, there doesn't appear to be much of a lip. It looks to be about 1/8". Way too thin.
Poor casting, improperly fitting T-nut, swarf or other junk under the tool post when it was "over tightened" etc. could all have played a part in what happened.
If you can't find another compound then welding may be the last resort.
But before I did that I would mill a new T-slot out of a block of steel, make it oversize. Mill out the compound to accept the oversize part and screw it down in there. It looks like there is enough material around that slot to do that.

Not sure what that hole is for in the front but it creates a weak point.

JL...................

J Tiers
03-11-2017, 06:40 PM
It's likely not too "dangerous", but it is likely to be fragile. Might get launched, might just throw pieces of broken compound around.

Looks like the whole thing was milled down to fit that post, is that a BXA or CXA? . You may simply be unable to use a QC post like that, due to a lack of room. The lips of the slot look like they would be too thin even if they were not broken.

If you did put 1/4" plate on it, either the post would maybe not fit, or the t-nut would not fit. Do you have a pic directly from the side, with toolpost and a holder in place, showing the end of the slot AND the tailstock all at once? That would give a good idea where you are at.

Joe_B
03-11-2017, 07:05 PM
I would inspect the rest of the lathe, you dont do that kind of damage without messing something else up.

BCRider
03-11-2017, 07:23 PM
Judging by the way the tool holder is sitting down so low that it seems flush to the bottom of the post itself I'm thinking that someone milled down the compound as well. And by doing so they didn't leave enough thickness.

The cutter side is pushing down. But the opposite side is pulling up. And the small residual amount of metal left is not all that much. And if it snapped out that much then what's left might be already damaged and just waiting to let go with a slight tug.

Clearly the tool post and size of the cutters being used is not a good fit for that size machine. I'd also second or third the suggestion to mill away the damaged area and repair it as suggested or by brazing on a couple of new slot lips.

The repair should be thicker than what is shown and after it's done follow up the repair with the replacement of that tool post for something more suitable to the machine.

Highpower
03-11-2017, 08:48 PM
Not sure what that hole is for in the front but it creates a weak point.

JL...................

Holds the indexing pin and spring for the original 4-way tool post.

1-800miner
03-11-2017, 11:51 PM
How dangerous is it? Well it got ripped out of there once, do you think it will happen again?

Dan_the_Chemist
03-12-2017, 12:59 AM
Do a cost/benefit risk analysis.

What is the chance it will fail, again? Probably somewhere between 1% to 50%.
What is the chance it will exit towards the operator? Probably 25 - 50%, especially if you see it start to wobble and make a grab.
What is the chance that it will do harm to the operator? Probably 90% to 95% ... it ain't gonna be nice.
What is the chance that it will hurt a lot? 95%
What is the chance of lost time? 80%
What is the chance of permanent injury? 10% to 40%
What is the chance it will kill you? 1% or less.

SO... now, figure out the costs of the losses...

Pain - I don't know, how much is being in severe pain for several days worth to you? Would you allow me to stab and mash your hand with a toolpost and cutting tool for $10,000 ???
Lost time - Assume you are out of work for 3 days. Will your boss understand? Will you lose pay?
Permanent injury - how much is losing a finger, or losing the use of your hand, or losing an eye worth to you? $10K to $200 K ?
Death - Well, most people behave as if their life is worth about $500K. Of course, if you have good life insurance you might consider doing your widow a favor...

So, multiply it all out... The chance of pain is about 0.1% to 20%... I'd put it on the higher end. If you are a gambling man, at 0.1% the expected loss for not repairing the lathe is only $10. If the repair costs more than $10 take the risk. BUT, at 20% the expected loss for not repairing the lathe is $2000. If it costs less than that, repair the lathe.

For permanent injury it's down to 0.01% to 0.04%... if you look at the negative payout, it's only a few bucks. The if I were a business owner risking your life, I'd go for it... And that is why juries assign penalties of over $10 million... At a potential payout of $10 M I'd be looking at a risk evaluated at around $1000 to $4000. Well worth spending the money to fix the lathe...

Same thing with death. The chance of death is really low... 0.001% or so... (of course these numbers are back of the envelope guesses, and could easily be wrong by a factor of 10). A gambling man would probably take the chance... But, if you have a wife and kids, you might want to consider how much it's worth it for your kids to grow up having a father... then again, the life insurance and re-marriage reduce that problem...

ME - I'd fix the damn thing before I used it. But I have an artificially inflated sense of self worth. I figure I'm one of a kind and pretty darned valuable.

It's up to you.

johansen
03-12-2017, 01:40 AM
I had a similar thing happen, except the bolt holding it to the compound broke. i was cutting something on the order of an inch diameter at maybe 500 rpm and the chuck would have had to exert about 500 pounds of force on the tool to snap the 1/4-20 bolt due to the leverage.

I was quite surprised the 0.2" thick cast iron the bolt was threaded into held.

Anyhow: its fairly likely that if such a thing were to happen, the tool post would be caught by the chuck jaws and something will break, given that the chuck and spindle has fairly significant rotational inertial. would it be launched at the operator? i doubt it. if it did, what velocity would it have? 100, 500 feet per minute? 500 fpm is a 10 minute mile, that's 6mph. when people look at a lathe they might ponder the velocity of the periphery of the chuck, which often exceeds the surface speed of the cutting operation by significant factor, but its unlikely for anything to be launched at the operator at that speed unless its caught by the chuck.

weird **** happens, its not really possible to imagine every possible failure mode.

Paul Alciatore
03-12-2017, 01:52 AM
My thoughts exactly.

And it does look like the compound was milled down for the tool post to fit. That was wrong, wrong, wrong. The tool post is the member that should have been milled down. If you do repair it as Toolguy suggests, I would leave the steel thicker and either get a new tool post or mill that toolpost down.




Not good. The remaining lips at the top are too thin and can break off easily. I would repair by milling off the broken parts and replace with 1/4" thick steel strips on each side with 3 or 4 flathead socket cap screws, then mill the assembly flat with a face mill or end mill. There is plenty of meat for the screws and the repair will last as long as the lathe.

Peter.
03-12-2017, 03:34 AM
I agree that it looks like the top's been milled to lower the height for the over-sized tool post. It need not be cutting forces alone that's pulled the top off but clamping forces too.

If I had to repair that and retain the use of that post I would mill off the remainder of the I would mill off the broken remains down below the top of the slide, mill the bottom of the slot deeper to accept the tee nut then either fix a pair of steel plates to form the top of the tee slot or make a single steel plate with an oval slot in it. A flat nut could be slid into the slot now and the bolt passed through the slot into the nut. Otherwise you could fit a square plate with a fixed-position bolt though it. Less versatile but more sturdy.

wierdscience
03-12-2017, 04:19 AM
Looks like familiar damage,many times this is caused by those crappy Armstrong round boring bar posts.All three lathes at work have had this treatment and all three have had the lips milled off and replaced with 1/2" thick flat bar held on with flat head Allen screws,four on each lip.

Baz
03-12-2017, 06:47 AM
There seems to be a fixation on having a T-slot. Why not weld a new holding bolt to a 1/4 or 3/8 plate and cut off enough of the top of the slide to ensure the oversize QCTP block is at the right height. If you didn't get a lot of toolholders it might still be worth getting a smaller size as the quantity of holders over time are the bigger investment.

flathead4
03-12-2017, 07:47 AM
I would take look at the t-nut. Can the bolt pass all the way through? If so, that might have actually been the cause of the damage to the compound. I have heard of strong t-slots being ripped out by a poorly designed t-nut let alone this compound that appears to have been thinned.

Tom

winchman
03-12-2017, 09:25 AM
The tool post might have been ripped out of the T-slot by running the screw on the tool post down through T-nut too far. That wouldn't damage anything else on the lathe. The T-nut usually has a deformed thread to keep this from happening, but it may have been removed when the T-nut was modified to fit the compound.

JoeLee
03-12-2017, 09:45 AM
The tool post might have been ripped out of the T-slot by running the screw on the tool post down through T-nut too far. That wouldn't damage anything else on the lathe. The T-nut usually has a deformed thread to keep this from happening, but it may have been removed when the T-nut was modified to fit the compound. If that were the case I think there would be visible signs of the bolt digging into the bottom of the slot. I don't see that.



JL.................

Stu
03-12-2017, 09:53 AM
There seems to be a fixation on having a T-slot. Why not weld a new holding bolt to a 1/4 or 3/8 plate and cut off enough of the top of the slide to ensure the oversize QCTP block is at the right height. If you didn't get a lot of toolholders it might still be worth getting a smaller size as the quantity of holders over time are the bigger investment.

I agree, get rid of the T slot

sawlog
03-12-2017, 10:49 AM
The repair depends on what method you feel comfortable with. Since I would use the quick change post I would mill a t slot as large as I could then fasten it to the compound with countersunk sockets head Allen screws as large that I could fit in the compound minimum of 4 or 6 if I could. Between the leftover cast iron and the oversized bolted t slot that should hold the quick change post


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A.K. Boomer
03-12-2017, 11:02 AM
It's likely not too "dangerous", but it is likely to be fragile. Might get launched, might just throw pieces of broken compound around.



Wow that was helpful --- which likely is more likely??? :rolleyes:

J Tiers
03-12-2017, 11:04 AM
AK47:

Too bad you didn;t like it, son....

Guess you missed the point. No use explaining it to you.

But the forces are not really in any direction to throw it into his face, which he was worried about. The chuck is pushing it down, not up. So it might just break out and maybe throw pieces sideways. The worst is probably to launch it out straight at low velocity.




Looks like familiar damage,many times this is caused by those crappy Armstrong round boring bar posts......

?????

Those seem no more likely to rip out the top than a wedge type QCTP. Actually LESS likely.

The wedge (or piston) posts have an inherent large overhang to the side, to which you ADD anything due to the bar. The round posts have the forces nicely centered, not overhung to the side. They normally have a larger t-nut than the hole seems to show, and the round post is of a good size, so it isn't so tippy as to have a lot of leverage.

I'd also not be surprised to find out it was a lantern post with the tool holder stuck out a mile and a half, as is usual. That would have a good bit of leverage, and it would be cocked and ready to break things when (not if) the person who does that suffers a dig-in of the wobbly stuck-out tool.

But given that ot appears someone milled it down to accept a too-large QCTP, it was probably just due to the big overhang of those posts along with a dig-in and maybe too much stick-out. Same thing that breaks off Atlas compounds, except this person did not have the compound run out all the way as is usual.

A.K. Boomer
03-12-2017, 11:35 AM
AK47:

Too bad you didn;t like it, son....

Guess you missed the point. No use explaining it to you.

But the forces are not really in any direction to throw it into his face, which he was worried about. The chuck is pushing it down, not up. So it might just break out and maybe throw pieces sideways. The worst is probably to launch it out straight at low velocity.




Holy man - so now we know what kind of work piece he has chucked up and what will happen to it when the QCTP "digs in"
or what position the chucks jaws are in when they "fail" and the work piece and jaw(s) gets "tossed" into the guys face,

or what RPMS the machine is going and how much stored potential kinetic energies are in play

or on - and on - and on...

yes please explain this incredible wisdom of yours, esp. with such an incredibly dangerous subject matter, one that could keep the guy from ever seeing his family again - or heading back into the house like nothing ever happened...

again one more time which likely is more likely ?

Oh I see you covered it with this statement;

"So it might just break out and maybe throw pieces sideways"

That's comforting - thank you for you in depth analysis ------ just love the words "might" and "maybe" when I got my face hanging out a foot or two away from a fast spinning 5lb work piece --- again :rolleyes:

Toolguy
03-12-2017, 12:13 PM
It looks to me like they milled down the compound slide to fit a bigger toolpost, then broke it out when the bolt went through the T nut and jack screwed it up. I have seen this happen a few times on mill tables with thicker metal above the T nut.

Upon further reflection, and reading other posts, I suspect the order of events went something like this: The original toolpost was most likely a 4 way revolving one, with a single bolt through the middle and no T slot. The remaining hole in the front of the compound slide is for a spring actuated plunger that would index the rotation of the toolpost every 45 or 90 degrees, or whatever positions were milled into the bottom of the toolpost. The center post would be stationary in order to keep the index areas in proper relation to the plunger.

At some point, someone decided they wanted to upgrade to a QC toolpost. All well and good, but they chose one too large for the machine. After removing the stationary bolt, milling down the top, and milling a T slot, they installed the new toolpost, but broke out the T slot in the process. This made the lathe fairly unuseable, thus the sale of it. Of course all of this scenario is no more than speculation and conjecture. The only usefulness may be if it helps someone else avoid the same mistakes in the future.

Chris Evans
03-12-2017, 12:41 PM
I was faced with similar damage on my second hand lathe but not on the tool post compound, mine was on the circular tee slot the compound swivels on. It had been overtightened and was a weak design/poor casting. My answer was to make a polystyrene pattern and get a new cross slide cast, a day on the mill and a day scraping in I now have a beefed up slide and I took the oportunity to increase thickness to add tee slots. New leadscrew and nut where made at the same time.

Tony Ennis
03-12-2017, 01:01 PM
In my inexperience (yeah you can probably stop reading now) I ask myself, is this good, or is this bad? To me it looks bad because another failure could throw a tiny chip of something into my eye. It doesn't have to be moving fast; it doesn't have to be large. The damage doesn't have to be permanent. Until I heal, I will perform my day-job inefficiently. and then there's the pain, suffering, and deductible. And time lost. And perhaps above all, the 'hold my beer' embarrassment because I ran a machine with a known broken part, and damn my bad luck, it broke in the same place AGAIN!

So mill it off and replace it with a piece of steel or cast iron. A pleasurable day of work. Or for me, week of work.

BCRider
03-12-2017, 01:17 PM
To those saying to fix it without a T slot I wonder if perhaps that is how it started out?

The Myford ML7 compounds don't use a T slot. Just a threaded hole for the funky clamping piece and the rocker saddle for the cutting bits.

It's possible that this one was the same way and a T slot was cut to allow using a different tool post. that might explain the thin and rather wide ears of the slot that broke out so easily.

It's also pretty clear from how the tool post is set up that the post itself is way too large for this machine. And likely that the tool bit itself is larger than the range of size between top of the compound and spindle axis is really intended to use. Thus the oversize tool in the over size tool post requiring the holder to be set super low and possibly to have required milling down of the compound in the first place.

J Tiers
03-12-2017, 02:18 PM
Would not putting a threaded rod on it severely limit the sort of toolpost that would be usable? I suppose if you know what you want to use you could make it to suit.

The idea of further milling off and putting in a few screws sounds as if it might, in the end, be little better than what was there. I suppose it would depend on how many, where placed, etc.

Sounds better actually to find another suitable compound on Ebay. That one has had the berries. There may not be much more material left under the skin we see; We already know about a big hole in the front, and there look to be holes in the "corners" under what is left of the t-slot.

Then the screw and nut have to have cavities under there as well, so without seeing the bottom, it is hard to guess how credible the idea of drilling out what is left of the material for screws is. Several of them might not have much material to go into.



Holy man - so now we know what kind of work piece he has chucked up and what will happen to it when the QCTP "digs in"
or what position the chucks jaws are in when they "fail" and the work piece and jaw(s) gets "tossed" into the guys face,

or what RPMS the machine is going and how much stored potential kinetic energies are in play

or on - and on - and on...

yes please explain this incredible wisdom of yours, esp. with such an incredibly dangerous subject matter, one that could keep the guy from ever seeing his family again - or heading back into the house like nothing ever happened...

again one more time which likely is more likely ?

Oh I see you covered it with this statement;

"So it might just break out and maybe throw pieces sideways"

That's comforting - thank you for you in depth analysis ------ just love the words "might" and "maybe" when I got my face hanging out a foot or two away from a fast spinning 5lb work piece --- again :rolleyes:

AK47... cut back on the coffee and No-Doz, it's a bad combination for you............. WOW, just WOW.

Oh, and stop making up stuff. The politicians do enough of that, and we are not supposed to get political, you know, so don't do what they do.

But you are correct, it is FAR too dangerous to run a lathe, better extend the controls robotically so you can stand behind armor. the motor and headstock might climb right up and chew your head off. Better safe than sorry.

The rest of us will go on as usual.

wierdscience
03-12-2017, 02:43 PM
AK47:

Too bad you didn;t like it, son....

Guess you missed the point. No use explaining it to you.

But the forces are not really in any direction to throw it into his face, which he was worried about. The chuck is pushing it down, not up. So it might just break out and maybe throw pieces sideways. The worst is probably to launch it out straight at low velocity.





?????

Those seem no more likely to rip out the top than a wedge type QCTP. Actually LESS likely.

The wedge (or piston) posts have an inherent large overhang to the side, to which you ADD anything due to the bar. The round posts have the forces nicely centered, not overhung to the side. They normally have a larger t-nut than the hole seems to show, and the round post is of a good size, so it isn't so tippy as to have a lot of leverage.

I'd also not be surprised to find out it was a lantern post with the tool holder stuck out a mile and a half, as is usual. That would have a good bit of leverage, and it would be cocked and ready to break things when (not if) the person who does that suffers a dig-in of the wobbly stuck-out tool.

But given that ot appears someone milled it down to accept a too-large QCTP, it was probably just due to the big overhang of those posts along with a dig-in and maybe too much stick-out. Same thing that breaks off Atlas compounds, except this person did not have the compound run out all the way as is usual.

I had it happen to me once on our big lathe at work.Most of those boring bar posts have a T-base that is smaller than the OD of the post.Add to that being a boring bar holder large offsets are the norm.One misstep in a blind bore and snap!Out pops some cast iron.With the QCTP most have a fairly large foot print and T-nut underneath.

I am also not sure how much if any the topslide was milled down,the lathe at work,despite it being a 24 x 120" machine had the typical cast iron T-slot lips,but they were only 1/2" thick.The thickness in the OP doesn't look out of place for a lathe that size.

A.K. Boomer
03-12-2017, 03:23 PM
JT just sit this one out - why? cuz it involves someone else's safety that's why - and not the only reason, more importantly is you don't have a clue, even if holding one end with only 1/3 the material was enough you did not take the piece down and get it magnafluxed to find out it it's not cracked in critical "remaining" areas from the last crash

Now if it were your face hovering directly above getting ready to "soak up" the momentum id say "knock yourself out"

but it's not - so your volunteering someone else's with bad advise...

take a chill and sit this one out....

J Tiers
03-12-2017, 04:19 PM
Weird: If it happens it happens. I believe you.

The one in question looks like a rectangular t-nut broke out. Seems like round ones take out more of a half-moon.

We do NOT know how far it filled the t-slot. One of the big problems with t-nuts is having them not go to the sides of the slot, so they pull up on more of the tip of the lip, and not full depth. That puts a biog bending moment on the lip, and might break it much more easily.


JT just sit this one out - why? cuz it involves someone else's safety that's why - and not the only reason, more importantly is you don't have a clue, even if holding one end with only 1/3 the material was enough you did not take the piece down and get it magnafluxed to find out it it's not cracked in critical "remaining" areas from the last crash

Now if it were your face hovering directly above getting ready to "soak up" the momentum id say "knock yourself out"

but it's not - so your volunteering someone else's with bad advise...

take a chill and sit this one out....

You are SO wildly off the planet. Not unusual, but..... you ARE hyperventilating a bit more than usual.

In any case, if you recall, I said it probably would fail. I doubt it will fly up and hit him in the face as he worries it might. Forces are wrong. More likely elsewhere, but even more likely less dramatic ... just as broken either way.

But if you read the last post, I think it would be better to replace not repair. With an unknown amount presumably cut off, and the evidence that it broke, it seems unlikely that it would get better. If Wierdscience is right and it was NOT milled down, it seems a pretty poor design with what appears to be very thin lips to the T-slot.

I wish the OP would post a pic from the side, that would show the general proportions, and give a lot better idea what the situation is. we HAVE asked for that.

And, I mentioned that it would probably break more if used as-is. ... guess you were so busy hyperventilating that you missed that. You are arguing that it will fly up and kill a guy. Seems doubtful, but it's not like it will work great as-is.

Note to self. Give AK47 a time-out on ignore.

legendboy
03-12-2017, 06:33 PM
Curious if you are in cow town?

A.K. Boomer
03-12-2017, 07:44 PM
You are SO wildly off the planet. Not unusual, but..... you ARE hyperventilating a bit more than usual.

In any case, if you recall, I said it probably would fail. I doubt it will fly up and hit him in the face as he worries it might. Forces are wrong. More likely elsewhere, but even more likely less dramatic ... just as broken either way.

But if you read the last post, I think it would be better to replace not repair. With an unknown amount presumably cut off, and the evidence that it broke, it seems unlikely that it would get better. If Wierdscience is right and it was NOT milled down, it seems a pretty poor design with what appears to be very thin lips to the T-slot.

I wish the OP would post a pic from the side, that would show the general proportions, and give a lot better idea what the situation is. we HAVE asked for that.

And, I mentioned that it would probably break more if used as-is. ... guess you were so busy hyperventilating that you missed that. You are arguing that it will fly up and kill a guy. Seems doubtful, but it's not like it will work great as-is.

Note to self. Give AK47 a time-out on ignore.

Wildly off the planet is what I would call this following advice that you gave;

But the forces are not really in any direction to throw it into his face, which he was worried about. The chuck is pushing it down, not up. So it might just break out and maybe throw pieces sideways. The worst is probably to launch it out straight at low velocity.


the QCTP could be the least of his worries, if the chuck AND work piece is forcing it down then the QCTP is forcing the chuck and work piece up,

so when the rear doves give way and send the tool bit into the work piece even more that's called a crash, and if it's big enough and he's using the external large diameter chuck jaws with minimum contact on a substantial hub piece that he was TURNING guess what gets launched into the face of the operator?

But don't worry everyone JT also stated that the pieces will get thrown and I quote "sideways"

yeah that's been my experience too:rolleyes: --- when dealing with centrifugal forces never stand sideways to the work piece - cuz that's where JT says the parts will fly, when in doubt and using broken equipment stand directly in line - that's the safest place :eek:
cuz remember and I quote; "The worst is probably to launch it out straight at low velocity"

thanks for making that call - even though you forgot to include the work piece that leaped out at 2,000+ rpms it's nice to know you did all that math on the QCTP and knew the geometry of the crash failure and engagement and are keeping everybody safe,,,

your amazing... always surprises me how much you know about everything...

J Tiers
03-12-2017, 08:00 PM
....
your amazing... always surprises me how much you know about everything...

And each time, you know just that little bit MORE, don't you?

https://en.wikipedia.org/wiki/Mirror

A.K. Boomer
03-12-2017, 08:06 PM
I usually agree with much of what you write JT, but sit this one out...

mattthemuppet
03-12-2017, 11:01 PM
You know, it has to be super offputting for new members to see a simple question degenerate into the usual wjlly waving pissing match

A.K. Boomer
03-12-2017, 11:24 PM
One mans pissing match is another mans safety concern, and reasons given as to "why" can prove to be invaluable,

so really don't see the newbies fleeing off somewhere because of it, in fact think they would be soaking it up as many who post have their concerns and much of it is around safety, realizing that it's not just the QCTP to worry about in a case like this is the first step in introducing analytical thinking --- and in this case every action has an opposing reaction - that could end up in your face... not a bad thing to talk about stuff like this.

J Tiers
03-13-2017, 12:11 AM
Well Matt/AK47. I appreciate your concerns.

In this case, the problems are completely different from being dangerous. It may or may not be dangerous. I don;t suppose it is any more dangerous than whatever happened to begin with (and for others who downplay the "incredible danger", see for example post 13...), but there IS a point to it.

We have here a machine that has been apparently milled down to fit an OVERSIZED toolpost. At least, several folks think it has been milled down, me included. The only good reason for that is to fit a toolpost that SHOULD NOT be on the machine. Or, I suppose, to remove damaged material and restore a smooth surface, but that suggests the damage was already weakening the part significantly, and that should have been thought about.

What was the result? It BROKE. Whether there was a too small t-nut or not, IT BROKE. Suggests that it might not be a good idea to do what was done. And that the thing was not very "safe" to begin with, since it broke. Is it worse now? There is less to break, so it probably won't take a lot to break it the rest of the way.

What lessons are there in the occurrence?

1) If you are going to modify a machine (which is not heresy or a death sentence to do) you should take a bit oif time to think about what is happening that you are not paying attention to... Are you going to thin-down some feature (t-slot lips here, it seems) that is important to the operation and needs to resist force? If so, what might happen?

2) When putting a fixture, a toolpost, a boring bar holder, etc, on a machine with a t-nut, it pays to look at the t-nut and the slot it goes into....

.....2A) Is the t-nut at least as large as the thing it is holding down? It won't hurt to have the t-nut at least 2/3 or more of the length of a compound slot. Filling it end to end is quite likely a good idea. That has the most holding power.

.....2B) Does the t-nut fill the WIDTH of the slot? If it does NOT, then you are asking the lips of the slot to carry a bending load, and they are usually cast iron, so that is not something they are good at. Better to fill the slot side to side, as nearly as you can, so the forces are a "shearing" load, and you get the maximum holding power.

3) When you tighten a t-nut stud, make sure the stud does not go clear through and start to "jack up" the t-nut. That can break the slot lips without much apparent effort. Make sure the t-nut is not threaded through, or damage the last thread so the stud will stop and not go through.

4) Look at the forces you are applying when you tighten down. On a milling table, it is common to have a t-nut in between the work and some sort of support for a "hold-down bar". The stud nut pushes down on the bar, the bar pushes down on the work, and the support. The t-nut pulls up on the table slot lips. Usually nothing is on top of the slot right there, so the lips get all the force.
It's better whenever possible to have the clamping force such that the t-nut is pulling up on the slot lips, and something on top is pushing down in the same spot. Then the t-slot lips are just being "squeezed", there is no "unbalanced" force on them. The only force on the slot lips is from something outside pushing or pulling on whatever is being clamped down.
That's not always possible, so pay attention to how hard you pull up when you cannot balance the forces. Often you can adjust the location of the stud vs the work so the t-nut is right next to the part being clamped, or even partly under it. A longer t-nut will spread the forces out and lessen the chances of breakage if you cannot get the t-nut under the work or support.

5) In the case of a lathe..... Avoid using a toolpost that is too large and sticks put too far. Avoid sticking the tool out too far. Make sure the work (and tool) is tightly held and will not shift take a much larger cut, and possibly have large forces suddenly applied to it. There is a decent chance this lathe had a "crash" or catastrophic "dig-in" that just levered a too-large tool or toolpost over, breaking out the weakened slot (assuming the compound was milled down).

Can breakage of a t-slot be dangerous? Of course. It's just one of the myriad of dangers in the shop. if you avoid having a breakage, then that danger is avoided. And it is cheaper not to have to repair damaged machines. The repair is often not as good as the original construction, and in any case it reminds you about your mistake as long as you have the machine.

mattthemuppet
03-13-2017, 11:20 AM
One mans pissing match is another mans safety concern, and reasons given as to "why" can prove to be invaluable,

so really don't see the newbies fleeing off somewhere because of it, in fact think they would be soaking it up as many who post have their concerns and much of it is around safety, realizing that it's not just the QCTP to worry about in a case like this is the first step in introducing analytical thinking --- and in this case every action has an opposing reaction - that could end up in your face... not a bad thing to talk about stuff like this.

You really think someone's going to read through all that hyperbole? Besides, I can't remember seeing the op again...

A.K. Boomer
03-13-2017, 11:28 AM
If your talking the post just before yours - No

if your talking shorter and to the point - Yes

Edit; you also have to keep perspective in mind, remember this is only 40 posts,,, big deal,,, this is the place that's racked up hundreds just in what color to paint your machine - or if an eagle can carry away a small goat, or how many chuck jaws are optimum - or the definition of "billet" aluminum...

Makes the OP's questioning seem downright important,,, might also introduce another topic --- "is all steel high speed steel if you get hit in the face with it?"

Dragons_fire
03-13-2017, 12:38 PM
Depending on what the rest of the compound looks like, what a about just filling the t-slot and putting one big bolt right through from the underside? Brian's post here shows exactly what I'm talking about on his busy bee lathe.

http://bbs.homeshopmachinist.net/threads/45701-Installing-AXA-100-QCTP-on-BusyBee-10-x-18-lathe

Dragons_fire
03-13-2017, 12:48 PM
Depending on what the rest of the compound looks like, what a about just filling the t-slot and putting one big bolt right through from the underside? Brian's post here shows exactly what I'm talking about on his busy bee lathe.

http://bbs.homeshopmachinist.net/threads/45701-Installing-AXA-100-QCTP-on-BusyBee-10-x-18-lathe

Thinking about this a little further, if it leaves enough meat, the top of the t-slot could be milled off a little lower and give the qctp a little more room so that the tool holder isn't hanging off the bottom.

Oyster
03-13-2017, 01:25 PM
Gentleman thank you for taking the time to reply. I learned an awful lot from this thread. I like the tool post I have and the idea of milling down the compound to accept a bolt straight through seems the best route. I'll have .375 of meat to hold the bolt. This will also drop the oversized tool post down to a workable height. Solving 2 problems with one operation is rare, and I'll take it. Here are some pictures of the compound. The one snag I see is the gib adjustment screw is proud of the surface I will end at after milling off the shoulder and lips of what makes up the slot for the tool post.

https://uploads.tapatalk-cdn.com/20170313/9b90687e07e6a011f5bbd00c91f3a6d4.jpghttps://uploads.tapatalk-cdn.com/20170313/c8618434e2db4fc6529a691ee3f5e210.jpghttps://uploads.tapatalk-cdn.com/20170313/0b48bdaec6dc83599430768533270eb0.jpghttps://uploads.tapatalk-cdn.com/20170313/2e87458e8ace2f50a2a4927325b2025e.jpg


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J Tiers
03-13-2017, 02:35 PM
OK, I think this MAY be a lot worse than we think. That compound appears to be VERY MUCH MODIFIED, and not in a good way.

I am starting to doubt that the t-slot was milled down in any way whatsoever.

Instead, from looking at pics, I think that someone PUT IN the T-slot where there WAS NEVER A T SLOT TO BEGIN WITH. And where it could not really fit.......

The pics I see of the machine seem to have NO t-slot. Apparently it had a hole for the 4-way toolpost pivot, which would also explain the other really odd features of the OPs machine. First, the index plunger hole, and second AND FAR MORE IMPORTANT.... the intersection of the gib screw with the t-slot. Third, the tiny lips of the t-slot.

I think someone MILLED IN the t-slot as best they could. It intersects the gib screw because there wasn;t any more room, so it had to. The t-slot lips are thin because that is all the space there was.

At this point, it is very difficult to decide if the whole compound should just be trashed and a replacement obtained, or if it is salvageable. It may be, but the slot needs filled in. Maybe a block can be brazed in place without messing up the rest of the compound too much. That would at least restore the material that seems to have been milled away when the t-slot was put in where it could not actually fit.

Manual
http://www.wttool.com/common/manuals/Td4A-5A_op-manual.pdf

http://img.photobucket.com/albums/0803/jstanley/TIDA%20107898_837ebfcfba7baf5992f548767e26d089_zps v0fkegb2.jpg (http://smg.photobucket.com/user/jstanley/media/TIDA%20107898_837ebfcfba7baf5992f548767e26d089_zps v0fkegb2.jpg.html)

http://img.photobucket.com/albums/0803/jstanley/TIDA%20107898_1bbce8016a332267120e632064c4cba4_zps v3z3g204.jpg (http://smg.photobucket.com/user/jstanley/media/TIDA%20107898_1bbce8016a332267120e632064c4cba4_zps v3z3g204.jpg.html)

Dan_the_Chemist
03-13-2017, 03:07 PM
A few months ago Lyle Petersen (MrPete222) published 3 videos about machining a replacement for a similarly damaged compound rest for an Atlas lathe.

http://i.imgur.com/mdcNtXm.jpg

You might find watching the three videos to be interesting. The first one of the series is:

TIPS #333 pt 1 Making a Compound Rest for a 6" Atlas Craftsman Lathe tubalcain (https://www.youtube.com/watch?v=fqPAFCRoCsQ)

The compound rest in your photos has 4 "teeth" remaining around a central broken out area. I wonder if the metal is defective? Are there small cracks in any of the 4 "teeth". Are the 4 "teeth" more likely to fail than similarly sized features made out of new metal? In the face of such uncertainty, I'd take the longer route and either replace most of that metal with new metal that has been welded in place, or I'd replace the entire compound rest. Yes, I am an old scaredy cat... then again, much of my career dealt with "high energy materials" (look up the euphemism) and I'm old with 10 fingers and 2 eyes.

Yes, the chances of receiving a major injury from using the old compound is probably pretty darn small. But I'd rather spend 2 days machining a replacement compound rest than take the small risk of spending 3 weeks healing to a "nearly good as before" state ... But, I might be over cautious. You make your own decisions.

Dragons_fire
03-13-2017, 03:25 PM
I think if you only take off the ~1/8" of the lip on the t-slot, and then braze in a filler piece and bolt right through. it looks like you could possibly take that 3/8" thickness to over 1/2" thickness.

No one has seemed to ask what you are using the lathe for? are you going to be using it for large diameter interrupted cuts, or for watchmaking in brass and aluminum? that would be something I would consider for how strong you really need it. I'm not suggesting underengineering it, but if you know youre only going to be doing small light cuts, there would be lots less stress on the compound than doing large interrupted cuts. Just something to ponder.

Oyster
03-13-2017, 03:53 PM
J, I think you're onto something. https://uploads.tapatalk-cdn.com/20170313/78db3052844116710a8d1f273c6620d7.jpg

Dan, I'm a firm believer in trying the easiest thing first. While I'm not against machining a whole new compound, I'd like to keep that as option b.

After milling out the lips and shoulders that make up the t slot I'll have .375 of material to play with. What does the hive mind here think of my sharpie drawn plan pictures here?
https://uploads.tapatalk-cdn.com/20170313/94d83425d87aa09fe4f59310efff99a0.jpg


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Oyster
03-13-2017, 04:04 PM
I think if you only take off the ~1/8" of the lip on the t-slot, and then braze in a filler piece and bolt right through. it looks like you could possibly take that 3/8" thickness to over 1/2" thickness.

No one has seemed to ask what you are using the lathe for? are you going to be using it for large diameter interrupted cuts, or for watchmaking in brass and aluminum? that would be something I would consider for how strong you really need it. I'm not suggesting underengineering it, but if you know youre only going to be doing small light cuts, there would be lots less stress on the compound than doing large interrupted cuts. Just something to ponder.

I'd like to be able to use the BXA QCTP that came with the machine because it's beefy and replacing it with comparable AXA and buying the same amount of tool holders I have for the BXA would cost me more than I have in the lathe itself. Machining the compound down like pictures above will allow me to keep my Dorian and will drop it down .450 putting my tool holders that much higher on the post.

I have an oyster business and I fabricate the machines I use. So what I use it for is hard to answer as the machines I build and maintain are all very different. Being in constant contact with salt I use aluminum, UHMW, and some stainless.


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The Artful Bodger
03-13-2017, 04:06 PM
Oyster, JT, although the manual diagram shows a slide with no T-slot the one it does show has no upstand either, apparently the slide in hand is not the one in the manual and may not have been modified.

I would mill off the broken edges to make everything tidy and make a piece to neatly fill the space and drilled and tapped for a centre post. Hold the new piece in place with screws being careful not to blunder into the dovetails.

Maybe braze the piece in.

BCRider
03-13-2017, 04:36 PM
You need stability and you need rigidity. The two are not the same but both are as important as the other. So some form of filler piece that is well attached over as much surface area as possible is a method to be encouraged. And that means something like silver solder or brazing or at least an array of numerous smaller size fasteners to basically "sew" the filler and new top surface into place. This would tie in with the rest of the stop slide to a far better degree. Particularly if you wish to to lower the top surface to allow using that oversize tool post.

My own feeling is that brazing or silver soldering would be the better option. But doing so will require some major heat source and proper pre-heating. I'd also suggest that you would be wise to find a piece of cast iron for the filler instead of steel just so the thermal expansion coefficients are more closely matched. Or at least do some homework to determine how close the expansion coefficients are between cast and some common mild steels.

The issue with just cobbing a filler in with four or six screws is that the rigidity of the body is cut down when you machine away the broken metal by making the part thinner. And adding a filler with minimal attachment points won't fully restore the original rididity. So I'd want to look at more fasteners of a smaller size to lock the filler down in more spots. Something even as small as 8-32's if I could fit up around 10 or so in key locations. The idea being to treat the joint more like a riveted seam in an aircraft where the seam was as strong and rigid as the base metal to either side.

I'd perhaps look at combining the lots of smaller screws around the edges and with a pattern through the middle with an industrial adhesive like Loctite 680. The combined result of these two steps could well be on par with the brazed in place filler for strength and rigidity. And might well rival the original one piece block of cast iron before it was slotted out.

The screws and adhesive method would also have the advantage that it could be done in the home shop instead of finding a welding shop with a heat source suitable for bringing up the whole casting and filler to brazing temperature in a fairly stress free manner. I'm sure a job like that would not be cheap.

J Tiers
03-13-2017, 04:38 PM
One of your "X'd" areas is where the gib screw goes. You probably want to retain that and leave a space for the screw to move into as on the original.

I'd not remove any but the broken material, leaving the two "shoulders", then add a filler block, preferably securing it in some way such as brazing. If brazed you can have the stud thread into the filler, instead of having it go deeper into material that was not drilled out to begin with.


Oyster, JT, although the manual diagram shows a slide with no T-slot the one it does show has no upstand either, apparently the slide in hand is not the one in the manual and may not have been modified.
...
Maybe braze the piece in.

I clearly believe it has been modified. re-read the differences, and look at the part, as well as the machine pics. Some DO show an amount of "upstand", not as much as this one, but some. Look at the second pic I attached above.

1) No designer in their right mind will have the gib adjuster interfere with the t-slot. Especially when threaded thru into space. That's #1 on the hit parade. But the OP's unit has that.

2) No pics seem to show a compound like this with any sort of a t-slot

3) the indexer hole is clearly the one for the stock toolpost in the manual. But that isn't the way the compound is now configured

4) The t-slot is made in just the way one might expect if it were added into a too-small space, such as adding-in a t-slot that should not be there.

Result is that there is hardly any more metal left in some places. Added modifications need to be oriented at adding back metal, not removing any more. I DO agree about brazing in repair metal. Seems reasonable and effective.

Brazing in material could put back the missing material and return the part to something similar to what it was originally.

Oyster
03-13-2017, 04:58 PM
Obviously a mock up using materials laying around but is this the alternative to brazing?

https://uploads.tapatalk-cdn.com/20170313/664f92fcde4992804f9c0b8b69c91ab0.jpg


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BCRider
03-13-2017, 05:21 PM
I think you'll be amazed at how those thin flat pieces will flex. Frankly I'd step away from the T slot idea and go back to the solid area with the single hole. That'll give you far more proper support for the QCTP but still leave you with options for other tool holding ideas that are not compatible with the QCTP body for whatever reason.

Since I posted the idea of multiple smaller size screws and Loctite 680 I'm really liking the idea. It keeps this down to being a home shop and thus frugal cost method.

Part of achieving a good working repair that is rigid and strong is not having light parts that flex and not having air gaps which reduce support for the repair piece. With that in mind my approach for a "lathe only" fix would be to set up the face plate or possibly use the four jaw chuck to hold the compound body. This would require making up some form of temporary tool rest to allow holding a cutter at the right height off the cross slide. How you do that will depend on what other tooling and materials you have at hand.

I'd face off the tool post area down to the depth of the T slot. This will mean cutting slightly into the shelf on the rear half of the body. But I'd only cut into it so far and leave a little of the back corners of the raised area. No need to remove more of the original metal than needed. With that in mind I would not center the cut on the original hole location. I'd make it out futher if at all possible. This will cause the body to be way off to one side and likely the restriction will be how far off to one side you can make it go without hitting the bed. Of course it'll be WILDLY out of balance. So that's where using the faceplate comes in since you could then counter balance it to at least allow using the slowest direct speed. Otherwise you'll need to run it painfully slowly. If you could find someone with a mill that would be WAY better.

Since you want to use the oversize tool post I'd then add a piece of 1/4" steel as a riser pad that is "stitched" to the body with at least 8 small screws and the Loctite 680. More like 12 would be better. And you'll want to skim the repair to ensure the top is smooth and parallel to the ways on the bottom of the slide. Again that's where the faceplate would be the chucking method of choice. Then a hole for the center stud would be drilled and tapped.

You don't NEED to stay with the stud that came with the tool post if it is not a common thread size. You want something that has some degree of universality to it for future shop tool posts that may not work well with the Dorian body.

Have you tried to track down a replacement compound body? In the end that may be the best option if you can source a replacement. Stick with the threaded hole and then turn the top down so you can use the over sized tool post. Call it a day and you're done.

BCRider
03-13-2017, 06:01 PM
I had another thought for you if you don't have a mill available. If you can set up an angle plate clamped to the cross slide and squared up to the spindle you could clamp the body of the compound to the face of the angle plate and make up a flycutter to be held in the chuck. That would allow you to make remove and face off the damaged area and down to the bottom of the T slot. And that way the cut could be neatly squared up right to the transition of the rear shelf of the top of the body.

Of course all this would be really easy if you happen to have access to a milling machine.

Oyster
03-13-2017, 07:02 PM
Luckily I have access to a dirty old Bridgeport as well as a lathe big enough to turn my whole machine in. I appreciate everyone's input. Going to have some crap weather for the next couple days. Hopefully il make some headway on this and can post pictures of the finished product.


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boslab
03-13-2017, 07:38 PM
Thinking about it I think I'd cut a block to fill the mounting slot for the tool and fix it, drill and tap right through for the toolpost stud, a longer would be needed, the slot is only there to mount the toolpost, mount it directly if you get what I'm talking about, the new mounting can be a flat headed bolt going right through and cleared at the back of the top slid.
Mark

quasi
06-09-2017, 02:42 PM
I had a Tida like yours with a longer bed. Good Lathe, Taiwan made.

techonehundred
06-09-2017, 04:00 PM
I have the SELECT branded version of the same lathe. I went ahead and milled off the t-slot because the top of the t-slot was .300 below center and the quick change tool post was almost impossible to use. To attach the post, I just drilled and tapped the compound and screwed the stud in. I know that it does not let me slide from side to side, but the clearance I got being lower made the Lathe much easier to use. It has been this way for almost 10 years with no problem. Just my $.02.

kendall
06-09-2017, 04:26 PM
Been looking at this, think turning the T slot onto a dovetail, machine a matching plate with a good snug fit and hard solder it in position. Then install strips on the top.

John Stevenson
06-09-2017, 04:33 PM
Gordon Bennett two pages of hot air.

Just put the compound away for the odd time you need to cut a taper very gently and in the meanwhile mill a solid block out of steel or Durabar to replace the whole compound.
Result is you get a deeper slot and can use your existing post

quasi
06-09-2017, 05:15 PM
Gordon Bennett two pages of hot air.

Just put the compound away for the odd time you need to cut a taper very gently and in the meanwhile mill a solid block out of steel or Durabar to replace the whole compound.
Result is you get a deeper slot and can use your existing post

Who the Smell is Gordon Bennett? Is he an Eddy the Eagle impersonator.?:p

CalM
06-09-2017, 05:58 PM
Gordon Bennett two pages of hot air.

Just put the compound away for the odd time you need to cut a taper very gently and in the meanwhile mill a solid block out of steel or Durabar to replace the whole compound.
Result is you get a deeper slot and can use your existing post


This is the BEST solution.

Compounds in general are just another joint to flex ......

But at times the angle motion is handy. Those times are not often.

Also on a small lathe, what does a tee slot buy you that a simple stud up from the bottom lacks? 25mm of back and forth? Worth little in my experience.

velocette
06-09-2017, 07:33 PM
Gordon Bennett two pages of hot air.

Just put the compound away for the odd time you need to cut a taper very gently and in the meanwhile mill a solid block out of steel or Durabar to replace the whole compound.
Result is you get a deeper slot and can use your existing post

Hi Thanks John for a great solution. Sorry in advance Now can I pinch your idea and say Fabricate a new top slide with a solid top without the slot and either drill and tap for a stud or a captive bolt from underneath.
Agreed that without the top slide gives a far more rigid setup.

Eric

J Tiers
06-09-2017, 08:28 PM
Eh a couple people already suggested just replacing the crosslide.

Make one? why not just get on ebay....? someone is bound to be selling one actually for that machine. And the toolpost that goes with it. Then it is just money and not a lot of work

Using a big block is another idea... less versatile, but certainly solid. And the weight of it would cut down on the chatter the machine probably has anyway.....