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View Full Version : Gettint a "set-tru" chuck to stay true?



jacampb2
12-25-2009, 11:11 PM
I have a 10" buck set true scroll chuck for my lathe. It is currently my only chuck, and is in good condition. The problem is that the chuck walks back of 0, and it is driving me nuts!

I tighten the opposing grub screw as tight as I can with a 18" ratchet, I tighten the face screw that lock it to the back plat as tight as I can in a star pattern. Zero is good as long as I take care with my tightening sequence. The issue is, take one even slightly interrupted cut and it starts to run out. Am I doing something wrong? Is there a way to make these things stay reasonably zeroed? I realize it is only going to be "perfect" at the diameter it was set with, but this can happen even during the same part w/o disturbing setup.

Thanks,
Jason

fasto
12-25-2009, 11:34 PM
I've a 6" Pratt-Burnerd adjust-true 3-jaw chuck that I use when doing runs of things too big for collets. I frequently work with 4 1/2" PVC rod in this chuck, running low speeds & heavy feeds, sometimes hard enough to explode the parts or throw them out of the chuck. I have never had the chuck's adjustment disturbed by these, ah, issues.
I don't tighten it nearly so tight as you indicate, either. Were I you, I'd have the chuck & backplate apart to check for burrs, chips, and such and also to find out if the chuck is drawing up tightly against the backplate when the front screws are tightened.

TGTool
12-26-2009, 12:12 AM
I've got a non-genuine set tru (Taiwan maybe) that works fine for me. The bolts holding the chuck to the backplate are snugged but not seriously tightened. I never touch them when adjusting centering. I don't put nearly as much torque on the adjustment screws either - just a little more on one if I need a thousandth or so, loosen the opposite if I'm out several thou. I'm wondering if you've got a lot of stress set up with tightening that gets re-distributed under load. No support for this suggestion, just hypothesis.

nheng
12-26-2009, 12:12 AM
The grub screws are only intended to push on the "hub" for centering purposes. I suspect that by tightening them, the screws at 90 degrees from the others are fighting to prevent movement and then with any cutting forces, the chuck jumps to a more favorable position. Gently snug the grubs only for centering and then tighten the face screws to maintain that position. Den

jacampb2
12-26-2009, 12:14 AM
One of the first things I did when I got the lathe (and chuck with it) was to completely disassemble the chuck clean and lube the scroll, and cleaned the chuck and back plate. I'm not saying it might not be full of crap again, it has seen about two years of intermittent hobby use, but it has done this from the first time I ever zeroed it.

Originally I did not tighten anything to the extent mentioned above, I have just gradually cinched it down more and more every time it drifts off...

I'll pull it apart and check its condition. The biggest issue arises when the sucker does not make it through a whole job.

Thanks,
Jason

jacampb2
12-26-2009, 12:20 AM
The grub screws are only intended to push on the "hub" for centering purposes. I suspect that by tightening them, the screws at 90 degrees from the others are fighting to prevent movement and then with any cutting forces, the chuck jumps to a more favorable position. Gently snug the grubs only for centering and then tighten the face screws to maintain that position. Den

How loose do you take the face screws? I typically just lightly break them loose (I know this is subjective, I should throw a torque wrench on it) and then adjust and tighten them back up. Any time I have tried to just lightly adjust the grubs just to center it, then when I tighten down the face screws, I find I am out again. I am assuming this is due to the chuck tilting a bit perpendicular to the spindle and then when I pull the chuck tight to the back plate it gets pulled parallel to the ways and the run out is back.

I need to get this thing virtually perfect to finish up my high speed spindle head. I need to turn an arbor for the router drive gear, the last one was out a few thou and it nearly destroyed itself when I bumped the router on...

Thanks for the advise guys. Keep it coming if you have any more thoughts!

Thanks,
Jason

Forrest Addy
12-26-2009, 12:46 AM
Consider this: three jaw chucks have limitations that have to be factored into the productivity equation, even adjustable three jaws chucks. The chuck is adjustable so you can tweak it when you need extra close concentricity Normal operation imnclidees having to adjust the work concentricity if drifts a little under heavy cuts or after changing work diameter.

The chuck should ordinarily grip reliably under all normal work conditions but there are exceptions related to material stability, thin walls, short grips, large overhangs, heavy cutting forces, and so on. If the work requires refined concentricity there hould be a point before the first finish cuts there the operator hould make a concentricity check.

Also hard jaws are slippery. If the surface available for gripping is of short aspect ratio perhaps soft jaws affording an enveloping grip should be considered.

I'm not poo-pooing your problem statement. I'm pointing the hitches and considerations in the way of simple progress from raw stock to finished part.

DR
12-26-2009, 01:05 AM
Hard to say whether the problem is your chuck or not. But, I can say for sure the Buck set true's are crap compared to the P-B equivalents.

Even a light crash on a Buck and it's toast.

Black_Moons
12-26-2009, 01:11 AM
Did you add any oil/grease after cleaning the chuck?

Purists say it must be 'clean and oil free!' to hold firm.

I hate the idea of 'clean' steel myself. Spells rust in my book.

maybe clean it and recoat with a more protective but less lubracating formual. like LPS3.

jacampb2
12-26-2009, 01:18 AM
If the work requires refined concentricity there hould be a point before the first finish cuts there the operator hould make a concentricity check.

Can you expound a bit on how to do this? Keep in mind that this bulletin board and books are my only source of education on machining in general. I don't even have the slimmest clue as to how I would measure for concetricity.


Hard to say whether the problem is your chuck or not.

What else might you think it could be?


Did you add any oil/grease after cleaning the chuck?

Purists say it must be 'clean and oil free!' to hold firm.

I hate the idea of 'clean' steel myself. Spells rust in my book.

maybe clean it and recoat with a more protective but less lubracating formual. like LPS3.

Actually, it had about 10 lbs of grease in it which had all flung to the outer edges. If I remember correctly, I sprayed the scroll w/ thin film lubericant. The jaws do not loosen, are you thinking that stuff in the scroll causes the zero to drift?

Thanks,
Jason

Black_Moons
12-26-2009, 01:32 AM
No I think the stuff thats leaked onto the surface beween the chuck and its backplate is what causes the zero to drift, the rest of it can probley stay in there :)
the scroll afaik is not designed to hold the chuck in zero, just move it while the front bolts are slightly loose.

tdmidget
12-26-2009, 01:49 AM
I'm with Tgtool here. You are wayyyy overdoing it. Take apart and clean and deburr. The clamping screws in the face should be tight enough to hold it flat and still allow adjustment with the adjusting screws on the OD. You might check and make sure that the plunger like pieces under the adjusting screws are there. I used to do aircraft turbine parts on these and had to be with in .0005. No problem at all. The way you are tightening things here tells me you may have sprung jaws. damaged scroll, etc. These are precision tools and should be treated as such.

DR
12-26-2009, 01:53 AM
.................................................. ......................

What else might you think it could be?

.................................................. .....................



The chuck mount to the spindle.

The jaws (out of square).

The operator (you don't need exceptional tightening of any of the screws).

As I said, with Buck's even a light crash and they're toast. I have a six and eight that can be trued, but will only stay for a part or two. Both were mildly crashed and still appear like new.

coldformer
12-26-2009, 01:55 AM
i have many times had set screws self descruct ,first thing i would check

JRouche
12-26-2009, 02:07 AM
The issue is, take one even slightly interrupted cut and it starts to run out. Am I doing something wrong? Is there a way to make these things stay reasonably zeroed? I realize it is only going to be "perfect" at the diameter it was set with, but this can happen even during the same part w/o disturbing setup.

Thanks,
Jason

Im not gonna say the buck chucks arent nice. But I have had issues with the jaws not locking down consistently. And I dont expect much from my scroll chucks. But I do expect a certain amount of consistency. Or actually holding ability.

I have two small lathes and had a nice Buck chuck. Did all I could to keep the jaws from pulling the work as I gripped it. I may have had a bad scroll, but I tore it down and cleaned it up, still issues..

Then I bought a Pratt Burnerd chuck for one of the lathes. WOW!! What a difference. And it wasnt a PBA chuck but an import, used stuff. The jaws locked down square to the work at all diameters. I was impressed. Got another one for the other lathe. Same thing. Solid chuck. Then got a couple 6 jaw chucks and now thats all I use for scroll chucks on the two lathes. The PB chucks are both steel body chucks and the three jaw is a "semi" steel body I think, what ever semi steel is :) Im sticking with the PB chucks for scroll chucks. Although. Got a nice brand new SCA 3 jaw chuck that is really nice but I keep the PB 6 jaw on the lathe so the SCA is outta the loop. JR

Glenn Wegman
12-26-2009, 06:42 AM
I tighten the opposing grub screw as tight as I can with a 18" ratchet, I tighten the face screw that lock it to the back plat as tight as I can in a star pattern. Zero is good as long as I take care with my tightening sequence. The issue is, take one even slightly interrupted cut and it starts to run out. Am I doing something wrong?
Thanks,
Jason

Yes.....

As nheng mentioned, get off of the grub screws, they are to align it, not re-shape it!

I have two set-tru's, a 6" and an 8", and neither have moved in years. I aligned them, tightened the face screws, then backed off the alignment screws, and then just lightly and evenly snugged up the alignment screws using the short length hex key that came with the chucks.

Neither have ever had more than .0003" TIR since I have owned them.

nheng
12-26-2009, 07:43 AM
One thing that REALLY helps with aligning my Rohm set-tru is the use of 2 hex wrenches on diametrically opposite grub screws. While watching an indicator, the 2 wrences, turned sort of in tandem, let you adjust centering without overtightening the grubs.

Rohm and I believe Buck both specify tightening the face screws when done to lock it in place. They should not permit movement. Den

JCHannum
12-26-2009, 08:05 AM
Another vote for the Buck chuck. I have two, 6" & 8" and have not had a problem with either shifting. They do not necessarily hold zero over a wide range of diameters though and this is to be expected.

I also think that the overtightening might have something to do with the problem. When the chuck is dismantled, check the spigot on the backplate the grub screws bear against to make sure it is round and not multifaceted from the action of the screws. A light skim cut to clean it up will not hurt anything.

Also check the fit of ID the scroll on the center post of the chuck. Wear here will allow the scroll to float and cause poor repeatability. In some cases, the scroll can be shimmed or sleeved to tighten it up. I suspect there are other non-Buck related problems causing the shifting.

Any of the adjust-tru chucks are not substitutes for four jaw chucks, but give a very limited range of adjustment. I recall something like +- 0.003" but don't quote me. If looking for more than this, the chuck is not capable of adjusting.

When all is said and done, it is still a three jaw chuck. When looking for the highest precision, nothing beats turning between centers.

Glenn Wegman
12-26-2009, 08:28 AM
Are you sure your jaws are not sprung?

If you tightened the aligning set screws with an 18" wrench, how long is the pipe you use on the chuck wrench? :)

Carld
12-26-2009, 10:42 AM
A shop I worked in had a Buck chuck and it was murder to use. I finally tore it down and found it buggered up where the set screws worked on the surfaces. Someone had replaced the smooth faced screws with the sharp ended ones and that caused problems.

I had to remachine the surface to remove the damaged area and then made a set of screws with smooth faces and after that it worked real nice.

I am with others that said over torquing the screws to move the chuck side to side will cause all kinds of problems. They are to move the chuck and keep it located just as those on a tailstock and are not meant to be over tight. The bolts on the face actually hold the chuck in place. If you can't adjust the chuck with short allen wrenches something is wrong so fix it.

I will say I don't like adjustable chucks, I just use a four jaw if it has to be that close. My 3 jaw will repeat on GTP bar within .001-.003" and if I rotate and chuck it several times I will find the sweet spot of .000-.001" and stop hunting.

JCHannum
12-26-2009, 11:16 AM
A shop I worked in had a Buck chuck and it was murder to use. I finally tore it down and found it buggered up where the set screws worked on the surfaces. Someone had replaced the smooth faced screws with the sharp ended ones and that caused problems.

I had to remachine the surface to remove the damaged area and then made a set of screws with smooth faces and after that it worked real nice.

Buck chucks have a plug between the set screw and the spigot to prevent damage from the setscrew.

Carld
12-26-2009, 11:20 AM
I guess they got removed before I tore it down. There was nothing between the screws and the surface they worked on.

spope14
12-26-2009, 03:03 PM
I have had pretty good luck with set-tru chucks, though mostly Bison. Two older Buck Chucks, they have proven very stable in the indicating and holding true department.

What type of chuck mount to spindle are you using? Mine are all D1-3. For a D1 type you need to have a constant index point, or to clarify, when you indicate the chuck true, mark a spot on the chuck and the spindle (dykem, marker, or after a while a vibro scribe). Line them up each time when putting the chuck on, or you will never get consistency with indicating.

jacampb2
12-26-2009, 07:56 PM
Okay, I get the point! I'll check out the back plate, and make sure it isn't scared up, that actually makes the most sense to me. I can't remember if the thing had the little brass plugs or not when I had it apart last.

As for the chuck jaws being sprung, I only use the T handle that came with it to tighten it. The ratchet for dialing it in began simply as a matter of convienience-- I'd rather turn a rathechet 5 then keep re-keying an allen wrench.

As for the spindle mount, it is an L1 mount, and the chuck can only go on in one orientation.

Thanks,
Jason

clutch
12-26-2009, 08:05 PM
I have a 10" buck set true scroll chuck for my lathe. It is currently my only chuck, and is in good condition. The problem is that the chuck walks back of 0, and it is driving me nuts!

I tighten the opposing grub screw as tight as I can with a 18" ratchet


The grub screws are for adjusting, not holding.



I tighten the face screw that lock it to the back plat as tight as I can in a star pattern. Zero is good as long as I take care with my tightening sequence. The issue is, take one even slightly interrupted cut and it starts to run out. Am I doing something wrong?


I think you are setting your self up for failure when you muscle the adjusting screws. All that locked up stress is looking for a reason to let loose, like during an interrupted cut.

I line up all sorts of chucks on cnc's and ID / OD grinders. The adjusting screws never should have to need severe torque on them if you are doing it right. I only put enough torque on them to keep them from falling out.

Clutch

jacampb2
01-11-2010, 02:10 PM
Well, over the weekend, I took the advice and pulled the chuck from the back plate. The dog screws had indeed marked the back plate, but not as bad as I was expecting. There was still a plug in each screw hole, looks to be cast iron, not brass. I took a skim cut on the back plate to true it up. Set the chuck up again and am still having a bit of trouble with it.

I spent over a half hour on it, and got it as perfect as I could, tightened the face bolts up that hold it to the back plate, and I am out .001". So, I just barely cracked the face bolts loose this time, went through it all again, and it seems a thou is as close as it is going to get.

I did not face the back plate while I had the chuck off, should I have? Is .001" simply as good as I can expect to get this thing? In all actuality, it is probably perfect for everything but the one project I am trying to do, the high speed spindle shaft for the router...

I actually ended up turning the shaft between centers, and that worked out excellent. In the last op though I bent it a hair, so I was screwed anyhow. I finally broke down and ordered a new pulley with a .25" bore, I'm just going to use a broken .25" EM for a shaft and quit screwing with the home made pulley and shaft...

Thanks,
Jason

Black_Moons
01-11-2010, 02:14 PM
Its all about the centers for the real accurate stuff :)

gzig5
01-11-2010, 05:18 PM
Stupid question, but do the threaded holes in the backplate go all the way through? Is one or two theads messed up? Might pay to run a tap through them. Is it possible that the bolts are bottoming out because they are not threaded all the way up to the head? I've got an old Buck 9" set tru on my L00 spindle that is no problem to get it to hold once in place. You might try backing the adjustment screws off after the front locking screws are tight and see if that has any affect. Make sure the locking screws have a little oil or grease.

Rich Carlstedt
01-11-2010, 08:14 PM
........... I took a skim cut on the back plate to true it up................
I did not face the back plate while I had the chuck off, should I have?
.........................
Jason

Jason
not sure of what you did ?
seems to conflict.
If you faced the step (big OD) you must face the general face the same amount, (assuming you have a step in the face)

What I would like you to do , is to remove the jaws, and remove the adjusting screws, then with a straight rod of brass or aluminum, push the scroll around through the adjusting holes.
I suspect the clamp screws on the face are not holding the scroll firmly.
now tighten the screws slowly and keep checking to see at which point
the scroll stops moving with gentle presuure.
If it still moves with the screws torqued to about 10 ft/pounds, you have a clearance problem. Also, when you find one screw clamps it, back it off and check the others individually. You may have only one screw functioning.
Also check to see if the threaded holes in the back plate allow the screws to go deeper . they may be bottoming before clamping !
If thats Ok, try it with the jaws inserted and see if any changes occur.

Thsi might point out a problem

An earlier poster mentioned that his chuck lost its setting after a crash..
Guys, all machine tools loose their settings after a crash.
Do it on the mill, and you will find the vice moved, or the tram is off
Even heavy cuts can produce this effect. Never ever expect a tool to be trusted after a crash..."If it's adjustable, it will move "
taking it for granted leads to nothing but scrap

Rich

J Tiers
01-11-2010, 08:51 PM
I have a nice little 4" Buck. it adjusts great with the setscrews, and I NEVER tighten the face screws tight.... just snugged.

The face screws CANNOT hold the chuck centered..... they WILL let it walk around. If it hasn't happened to you, you are just light handed, or else lucky. For now.

it takes BOTH screws to hold it in place.

And 0.003" range is nuttycakes...... I have a total movement of about 0.020 possible, centered around "center".

And only within 0.001"? you should be able to as well with teh chuck adjustment as with a 4-jaw. Maybe better, the threads are a lot finer.

As for the problem chuck......

1) the jaws sound like they are maybe bell-mouthed. if so, go ahead and grind them. bell-mouthed jaws mostly won't hold a part straight for more than a few seconds of cutting.

2) the set screws/plugs may be binding up and not allowing full adjustment or complete tightening.

3) the idea of a worn scroll also has merit...... shimming it can allow years of further use.

danlb
01-11-2010, 11:44 PM
I did not face the back plate while I had the chuck off, should I have?

The instructions that come with the chuck say that you must true up the mounting plate with a facing cut before you can use it.

IIRC,

1) mount the adapter.

2) Take a skim pass to true it to your spindle.

3) mount the chuck to the adapter

4) Go through the centering procedure.

Dan

J Tiers
01-12-2010, 08:55 AM
I did not face the back plate while I had the chuck off, should I have? Is .001" simply as good as I can expect to get this thing? In all actuality, it is probably perfect for everything but the one project I am trying to do, the high speed spindle shaft for the router...


if it was "out", you ought to have re-cut the seat anyway, the flat flange it sits on. If it was made decently, and your spindle is in good shape, you shouldn't have had to, although it may be a good idea for the ultimate in accuracy with it.

Spindles etc you will notice nearly always have centers in the ends. This is because they are ground on centers. Not in chucks. Centers are the ultimate, even a 4 jaw chuck is not as accurate and certainly not as repeatable.

Collets you say? Only if the entire collet setup was made perfectly. Otherwise a collet is just another form of 3 jaw chuck.

jacampb2
01-12-2010, 10:18 AM
I did not indicate the face, perhaps I should have. The only reason I took a skim cut off the circumference is due the the "dings" from the grub screws. The internal spindle taper in the lathe indicates about perfect, I've had the whole head apart and all the bearings are in good shape. I don't think it is a spindle/bearing issue, I'm pretty sure it is the chuck, unfortunately, it is the only chuck I have for this lathe.

I'd love to get more, but the L1 spindle nose is a bit of a setback, it is not that obscure, but it seems to go for extraordinary money, even used. Bison makes a back plate that is reasonable priced, and although I have found it on their website, I have yet to find a retailer that offers it.

I really need to learn how to single point thread, it is one machine op that I am somehow afraid of and do not understand. I would happily make my own back plates if I could thread them...

For now, the problem is solved as I ended up buying the parts to make the driven shaft and pulley. It cost me like $15 and in the end that makes it much cheaper than the ~3 days and several failed attempts of doing this myself.

Thanks,
Jason

Black_Moons
01-12-2010, 10:30 AM
what? afraid of threading?

buy some aluminum, one HSS blank and a fishtail gage, there your done the hard part now, next read a basic page about threading :) and realise its one of the sloowwestt operations you can do. dozens of passes at 0.001~0.005" or so cutting depth (Starting with deep passes and moving to lighter and lighter passes and more and more of the tool edge contacts the work)

Learn external threading first.

Doing 'inside' threading isent much more diffacult when you have a through hole and the hole is reasonabley big, you just buy a boring bar ($10 peice of steel with a hole in it designed to fit your HSS blank) and insert the blank into it and basicly do the same thing as you did learning how to externaly thread, except you don't get to see all the fun. and have to remember to 'retract' the tool into the work (forward) insted of away from the work (like you do when working externaly) for the next pass.

PS: Those cheap triangular carbide tools that say they can thread do not work except for on very low TPI threads due to the fact a triangular carbide insert does not follow a proper thread form.
Its REALLY easy to grind your own threading bit with HSS using just ANY kind of grinder (Dremel with 2" wide cutoff wheels could even do it! but an angle grinder, belt sander, bench grinder, etc would do much better)

jacampb2
01-12-2010, 10:46 AM
Yeah, I know I shouldn't be afraid of it. It seems like it should be simple. The L1 back plates are external thread, 6" 6tpi. I know I can grind the bit, I need to get one of the gauges, and every time I place an order from a tooling supplier, I forget the damn thing!