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KiddZimaHater
08-14-2010, 06:16 PM
For anyone with a 6" rotary table...
What size T-nuts do you use in it?
Are they the small 3/8ths T-nuts, or the larger 1/2"?
Just wondering. I'm gonna be buying a 6" rotary, and need to get 4 t-nuts to mount the chuck.

dp
08-14-2010, 06:38 PM
I made some t-nuts for my RT to fit existing 1/4" - 20 screws in a chuck I mounted. http://metalworkingathome.com/?p=156

They're made from 0.625 square section with a 0.250" high base, total height of 0.550", and the round section is 0.390". Drill and thread to suite. This RT came from Grizzly.

gnm109
08-14-2010, 06:58 PM
I bought a 6" Rotary Table from CDCO. It has 13mm T-slots so I had to make a set of T-nuts. I made one piece that fit into the slot and then cut it into segments. I drilled and tapped 5/16-18 for some studs. 13mm is the Asian equivalent of 1/2", I guess.

I also had to make table keys for it, since it came without them. They are 5/8".

From what I understand, there's no one size for these units. Some are larger and some are smaller.


http://i144.photobucket.com/albums/r188/gnm109/RotaryTableB.jpg

KiddZimaHater
08-14-2010, 07:17 PM
WOW! nice pic GNM109.
Since the sizes vary, I guess I'll have to be patient and wait till it arrives. McMaster-Carr has a bunch of different sizes listed. Or I'll just find a chunk of scrap and make my own.

gnm109
08-14-2010, 07:38 PM
WOW! nice pic GNM109.
Since the sizes vary, I guess I'll have to be patient and wait till it arrives. McMaster-Carr has a bunch of different sizes listed. Or I'll just find a chunk of scrap and make my own.


Yeah, you'd better wait and then make some. Those things aren't cheap if you have to buy them, either. I bought a Kurt D675 6" vise from Enco a while back. I wanted to use it on my Webb Mill which has typical 5/8" slots. Of course, it didn't come with the two table keys so I looked on the Kurt website and they want......$30.00!!!!!!! for a pair of them....cough, cough......

Enco was a little less at $29.95... LOL. So, I got another hunk of steel and whittled a pair of them out. They are a little tricky, too, since, for some unknown reason, they are 11/16" on the vise side and 5/8" on the table side and the slots in the vise are something like 3/16" deep. They are tough to hold when milling them.

I also have a Phase II vise that has 18mm slots in it so, apparently, we're on our own. LOL. :)


http://www.kurtworkholding.com/keys-11/16-p-965-l-en.html

dp
08-14-2010, 08:36 PM
Something to remember is the slots on a 6' table aren't very long so if you make true t-nuts, you may not be able to use the full length toward the center. They collide with the end of the slot long before the threaded section is at the useful limit. Hence my square nuts. I'm even going to have to round off one side to get an even better fit.

oldtiffie
08-14-2010, 09:39 PM
Dennis.

If I need them I don't do much milling. I turn a stepped/flanged cylinder - with the flange diameter a bit larger and its width a bit less than the widest part of the t-slot and the "neck" cylinder diameter a bit less than than the vertical slot and a bit shorter than it.

I then drill and tap it to suit and mill, part it off and then mill (or hand grind) two opposite faces on the flange to suit the tee slot.

It is all done on the lathe (all or mostly) and it covers the "rounded ends" requirement as well - all in one go.

With all t-nuts that have a removable screw fitted to them, it is a good idea to distort the bottom thread so as to prevent the screw hitting the bottom of the t-slot. I usually do it with a chisel or a hardened steel ball (about or just a bit larger than the thread nominal diameter).

Paul Alciatore
08-14-2010, 09:54 PM
Something to remember is the slots on a 6' table aren't very long so if you make true t-nuts, you may not be able to use the full length toward the center. They collide with the end of the slot long before the threaded section is at the useful limit. Hence my square nuts. I'm even going to have to round off one side to get an even better fit.

If you make them yourself, you can round off one end so they fit all the way to the end of the slots. I'm not sure how helpful this is as the clamps are usually long enough to reach close to the center anyway.

As for getting the nuts, the various suppliers usually have clamp sets available for reasonable prices. I have had good luck with the import/house brand sets: I got a 1/2" set for about $40 last year. It has six nuts and tee nuts, six clamps, three pairs or step blocks, and a bunch of studs. You may be able to get a 3/8" set for even less. But I did have a problem with the tee nuts as they did not fit the slots in my new mill. I had to buy a half dozen anyway. Oh, well. The 3/8" set I bought some years ago for my 10" RT did fit just fine. I also bought some 3/8" tee nuts to fit the mill table so I can use the 3/8" set there also.

BTW, one of the most useful extras you can buy for a clamp set is some extra, SHORTER studs. I have several sizes shorter than the shortest ones in the sets and they are the most useful. The longer ones get in the way of milling operations all the time.

oldtiffie
08-14-2010, 09:56 PM
.....................................

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

So, I got another hunk of steel and whittled a pair of them out. They are a little tricky, too, since, for some unknown reason, they are 11/16" on the vise side and 5/8" on the table side and the slots in the vise are something like 3/16" deep. They are tough to hold when milling them.

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


I don't like milling in a vise if I can help it - but if I have to I do it.

That 3/16" "grip" is a good case in point.

For that sort of job, I prefer to clamp the job to an angle plate where I can get a good "grip" and there is little chance of the cutter/load "pulling" the job.

I set the angle plate to the mill table axis as I would set a vice and then clamp a flat bar or a couple of "rounds" to the angle plate (set the tops of rounds or flat bar to be parallel to the mill table). Set the job onto the flat/rounds and clamp it.

It is very easy then to mill any material off and to keep it concentric as well as all that is needed is to roll the job over onto the flat/round. If done carefully, a quite safe heavy concentric cut can be made quite easily.

I prefer to mill with the job fixed/clamped to the table - but that isn't always feasible either.

A good solid accurate angle plate is a real asset if used to advantage.

gnm109
08-14-2010, 10:05 PM
I don't like milling in a vise if I can help it - but if I have to I do it.

That 3/16" "grip" is a good case in point.

For that sort of job, I prefer to clamp the job to an angle plate where I can get a good "grip" and there is little chance of the cutter/load "pulling" the job.

I set the angle plate to the mill table axis as I would set a vice and then clamp a flat bar or a couple of "rounds" to the angle plate (set the tops of rounds or flat bar to be parallel to the mill table). Set the job onto the flat/rounds and clamp it.

It is very easy then to mill any material off and to keep it concentric as well as all that is needed is to roll the job over onto the flat/round. If done carefully, a quite safe heavy concentric cut can be made quite easily.

I prefer to mill with the job fixed/clamped to the table - but that isn't always feasible either.

A good solid accurate angle plate is a real asset if used to advantage.


Yes, that would be an excellent method. If I do any more of them, I'll do it that way. I've got an angle plate.

Thanks!

dp
08-14-2010, 10:51 PM
When I made mine I put some square stock in the lathe chuck, bored and tapped it deep enough so I'd have 4 of them when finished, then turned down the round sections, then parted them off.

Tiffie is correct about corrupting the bottom thread - this keeps the screw from bottoming out in the slot.

oldtiffie
08-14-2010, 11:15 PM
When I made mine I put some square stock in the lathe chuck, bored and tapped it deep enough so I'd have 4 of them when finished, then turned down the round sections, then parted them off.

Tiffie is correct about corrupting the bottom thread - this keeps the screw from bottoming out in the slot.

Dennis.

I was surprised that you didn't use your shaper as t-nuts and dove-tails etc. are just "made" for doing on a shaper.

I should explain why the screws in a t-nut should not impact/contact the bottom of the t-slot.

If the screw contacts the bottom of the t-slot it will cause the t-nut to rise and "jack up" the "over-hangs" or "wings" on the mill table. Cast iron is notoriously weak in tension or bending - both are in action here - and the concentrtation of forces on/at the corner of the overhangs can actually cause the section of the overhang to "snap" and break out of/from the mill table. It is not at all unusual to see in milling machine tables - along with "dings" and drilled holes etc.

If the screw does not impact the bottom, the "wings" of the t-nut are only forced up when the job/vice etc. on the mill table is clamped in which case the t-slot "wings" are clamped/compressed between the wings of the t-nut and the under-side of the vise/job as the nut is tightened above the job/vise. In this case there is minimal bending stress on the table t-slot wings.

dp
08-14-2010, 11:52 PM
Dennis.

I was surprised that you didn't use your shaper as t-nuts and dove-tails etc. are just "made" for doing on a shaper.

I've done that, too, but these needed to be simple squares rather that true t-nuts. The shaper does a sweet job of getting the stock to the T shape quickly.

oldtiffie
08-15-2010, 12:29 AM
http://i144.photobucket.com/albums/r188/gnm109/RotaryTableB.jpg

Yeah, you'd better wait and then make some. Those things aren't cheap if you have to buy them, either. I bought a Kurt D675 6" vise from Enco a while back. I wanted to use it on my Webb Mill which has typical 5/8" slots. Of course, it didn't come with the two table keys so I looked on the Kurt website and they want......$30.00!!!!!!! for a pair of them....cough, cough......

Enco was a little less at $29.95... LOL. So, I got another hunk of steel and whittled a pair of them out. They are a little tricky, too, since, for some unknown reason, they are 11/16" on the vise side and 5/8" on the table side and the slots in the vise are something like 3/16" deep. They are tough to hold when milling them.

I also have a Phase II vise that has 18mm slots in it so, apparently, we're on our own. LOL.


http://www.kurtworkholding.com/keys-11/16-p-965-l-en.html

Thanks gnm109.

I "borrowed" your pic from another post on this thread.

I never use keys on my stuff that goes on my mill tables and only rarely on stuff that goes on my grinders.

Storing the stuff with keys under it is a PITA as it rocks and scratches and "catches" everything - mill tables included. This is particularly so with heavy rotary tables, dividing-heads and vises and the like.

If they are a "tight/neat" fit in the table slots, they jamb and can be a PITA to get in and out of the slots. They make a mean score across a table as well.

The underlying assumption seems to be that all milling table slots are accurate as regards alignment to the table "X" axis and that all slots are the same (width) as each other and through-out their length. There is an assumption too that the keys are in fact parallel to the vise jaws or the zero of a rotary table - maybe.

Maybe they are - but maybe they are not either.

Slots can be "bruised" by rough handling and t-nuts etc.

I lift my vise/rotary table etc. to the edge of the table, tilt it, lower it to the table and slide it to where I want it - which is much harder to do with "keys" fitted to the under-sides.

If I need to "angle" my vise or rotary table etc. on the mill table, I need to remove the keys anyway - unless I have a rotary base under the vise.

I prefer to set my vise etc. up by hand and indicator (or square or protractor or bevel guage) each time I set it up on the mill table. I set up to the degree necessary for the job in hand.

http://i200.photobucket.com/albums/aa294/oldtiffie/Seig_X3_mill/SeigX3_16.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Seig_X3_mill/SeigX3_21.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Seig_X3_mill/SeigX3_25.jpg

dp
08-15-2010, 12:46 AM
Here's the problem I'm solving with smaller non-T nutz. As seen, the bolt in the circle on the left is well off the inner limit of the slot. But what the heck is that other stud on the clamping foot in the right hand circle? :D

From Tiffie's picture above:
http://metalworkingathome.com/images/tiffiesRT.png

oldtiffie
08-15-2010, 01:06 AM
http://metalworkingathome.com/images/tiffiesRT.png

Dennis.

The "stud" on the right-hand side was just put in to hold the rotary table until I got around to finally clamping it.

The situation on the left could be resolved with a "round" t-nut - a spigot on a flange - with the two "flats" machined/hack-sawn/hand-ground" off to suit the wider lower part of the t-slot - to stop the "nut" turning.

Note that there is no key-slot for the vertical-mounting face anyway whereas there is such a slot in gnm109's rotary table.

http://i144.photobucket.com/albums/r188/gnm109/RotaryTableB.jpg

My criteria for my rotary tables were that they had 3 t-slots (not 4) and that they were "Vertex".

The 3 slots suit my front-face mounted 3-jaw chuck as well as my ER-32 adaptor for/from my lathe:
http://i200.photobucket.com/albums/aa294/oldtiffie/HF-45%20Mill%20misc/HF45-5.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/HF-45%20Mill%20misc/HF45-4-1.jpg

dp
08-15-2010, 01:36 AM
http://metalworkingathome.com/images/tiffiesRT.png

Dennis.

The "stud" on the right-hand side was just put in to hold the rotary table until I got around to finally clamping it.

The situation on the left could be resolved with a "round" t-nut - a spigot on a flange - with the two "flats" machined/hack-sawn/hand-ground" off to suit the wider lower part of the t-slot - to stop the "nut" turning.



Yep, yep, and yep. I knew it was only a setup pic to show a point but I thought I'd have a little fun. It's been so dark and brooding here lately, a chuckle here and there can't hurt.

I'll need to round off my square nutz to get that last little advantage, too.

oldtiffie
08-15-2010, 02:19 AM
Yep, yep, and yep. I knew it was only a setup pic to show a point but I thought I'd have a little fun. It's been so dark and brooding here lately, a chuckle here and there can't hurt.
I'll need to round off my square nutz to get that last little advantage, too.

I sort of guessed that Dennis.

If its like that in mid-Summer up there what's it like in mid-Winter (as it is down here)?

dp
08-15-2010, 02:46 AM
I sort of guessed that Dennis.

If its like that in mid-Summer up there what's it like in mid-Winter (as it is down here)?

This is America. We're all armed to the teeth, so we're well behaved in person.

Arcane
08-15-2010, 04:34 AM
I should explain why the screws in a t-nut should not impact/contact the bottom of the t-slot.

If the screw contacts the bottom of the t-slot it will cause the t-nut to rise and "jack up" the "over-hangs" or "wings" on the mill table. Cast iron is notoriously weak in tension or bending - both are in action here - and the concentrtation of forces on/at the corner of the overhangs can actually cause the section of the overhang to "snap" and break out of/from the mill table. It is not at all unusual to see in milling machine tables - along with "dings" and drilled holes etc.

If the screw does not impact the bottom, the "wings" of the t-nut are only forced up when the job/vice etc. on the mill table is clamped in which case the t-slot "wings" are clamped/compressed between the wings of the t-nut and the under-side of the vise/job as the nut is tightened above the job/vise. In this case there is minimal bending stress on the table t-slot wings.


Since this method of clamping anything down on a milling table is limited to specific cases such as a vise or RT where there are slots at table level to sandwich the tabs, I would have to call this explanation a myth.

Anytime you use a clamp set such as shown below, you are in effect lifting the edge of the slot with the same force that would be generated if the stud were to bottom out in the slot. Sometimes it just isn't possible to get the optimum clamping position you have with a vice or RT.

http://img.photobucket.com/albums/0603/Arcane/Saskatchewan%20Snowblower/th_B054.jpg (http://smg.photobucket.com/albums/0603/Arcane/Saskatchewan%20Snowblower/?action=view&current=B054.jpg)

If a person leans on the wrench with a 2 foot snipe or runs out of thread on the stud and continues tightening the nut down because the workpiece is still loose, chances are he will chunk out the slot, but that is well past the clamping force needed to hold everything I have ever milled on my BP clone. In fact, I use a Williams brand single-open engineer's wrench similar to this one (a #5, 8 3/8 overall length) and it is impossible for me to generate enough torque to harm my mill table slots, and believe me...when I put my fat behind a wrench, something moves!:D (Ain't saying what!) My workpieces never move around any either.
http://img.photobucket.com/albums/0603/Arcane/Saskatchewan%20Snowblower/th_williams_oe24_704_wrench_usa_f_cropped_w560_h19 6.jpg (http://smg.photobucket.com/albums/0603/Arcane/Saskatchewan%20Snowblower/?action=view&current=williams_oe24_704_wrench_usa_f_cropped_w56 0_h196.jpg)


I would say the real reason to have the interrupted threads at the bottom of a T-nut is simply to prevent it from wedging into the slot during use and making it a booger to slide along to position it.

oldtiffie
08-15-2010, 07:23 AM
Good discussion Arcane.

http://img.photobucket.com/albums/0603/Arcane/Saskatchewan%20Snowblower/th_B054.jpg

While I'd possibly agree with you in an ideal state, and assuming that the bolt was free-running in both the nut on top of the clamp and in the t-nut, it is quite possible that the screw will both be turning in the t-nut and the screw. When the resistance due to the force of the screw on the base of the t-slot is sufficiently large enough, the balance of the relative turning will be between the nut on top of the clamp and the clamp. In this case there would be some up-lift force on the t-nut and the "wings" of the t-slot in the mill table. If that were so the further the force due to the spanner on the nut on the clamp would reduce the up-lift force between the screw and the base of the t-slot via the t-nut. If that were so, the up-ward force on the wings of the t-slot might be reasonable.

If, on the other hand, for what-ever reason, the nut on the clamp was binding on the screw, a significant torque could be transmitted to the screw and t-nut and force the end of the screw into the base of the t-slot and so increase the up-lift on the t-slot wings.

In all of these cases, the up-lift to the wings is unduly increased without any more clamping force to the clamp and without the base of a vise or an angle plate or a rotary table base etc. directly over it to resist it.

You will quite often have the base of the t-nuts "swaged" such that the screw will not pass through it to the base of the t-slot. That resistance can be quite significant - for the reasons given.

Many "shop-made" t-nuts are tapped right through and left "as is" and some distorted/swaged threads on store-bought t-nuts are tapped out to "free them up".

Good clamping practice requires that the centre line (axis) of the clamp screw be as near to the job being clamped as possible or practical - and if part of the t-nut is actually under the packing or the job being clamped, then so much the better.

A clamp is essentially a first order lever:


Classes
There are three classes of levers representing variations in the relative locations of the fulcrum, the load and the force:[3]

Class 1: The fulcrum is located between the applied force and the load, for example, a crowbar or a pair of scissors or a seesawClass 2: The load is situated between the fulcrum and the force, for example, a wheelbarrow or a nutcracker.
Class 3: The force is applied between the fulcrum and the load, for example, a nail clipper or tweezers or human mandible

from:
http://en.wikipedia.org/wiki/Lever

see also:
http://www.dynamicscience.com.au/tester/solutions/hydraulicus/simplemachineslevers1.htm

http://www.google.com.au/#hl=en&source=hp&q=order+of+levers&aq=0&aqi=g3&aql=&oq=order+of+lever&gs_rfai=&fp=266f2fb68f6eb4c

In that case, all of the "pull-down" force is not transmitted to the job as it it is shared with the spacer/packer under the clamp. The nearer the screw axis is to the job (and the further away it is from the packer/spacer) the better as more of the clamping force will go to the job.

(Too?) many are inclined to over-tighten clamps which does not help the mill/machine table at all.

When I tighten a clamp nut I put my left hand over the ring (preferred) or open ended (alternative) spanner at the nut and pull steadily with my right hand/arm until the nut is "firm". I follow up with a "bump" on the end of the spanner with the heel/ball of my right hand used as a "dead-blow" hammer. Its amazing how well it works. (Same applies to tightening a vise or a draw-bar).

If I think that one or two clamps will not suffice, I never over-tighten them. I use any or all of additional clamps or table stops or put a sheet of newspaper between the job and the table.

Forrest Addy
08-15-2010, 08:18 AM
Standard T slots are pretty bulky when machined in a small mounting surface like a 6" rotary table. I'm of the opinion that small rotary tables are best arranged without T slots. I would prefer a plain flat top rotary table with a centering feature on it (a rabbet or a short taper) and a Morse taper in the center for locating spuds. Then have a half dozen thickish solid steel sub-plates to mount on it. One with a chuck, one with an X-Y slide (eh??), and the others blank for tapped holes as needed, or machining locatng features directly in the sub-plate - or tack weld directly to it!!

Attach the sub-plates with four #10 SHCS. A #10 heat-treated screw has a tensile trength of about 2500 lb. The sub-plates will go nowhere because they are positively located with a solid face mount and a rabbet. You really don't need big brutal hold-down bolts; lifting forces in machine work are typically small compared to drilling thrusts and side milling. You can also detach the sub-plates and move them mounted part and all to the lathe and back for further work.

gnm109
08-15-2010, 11:31 AM
I really need the T-slots on the rotary table as well as on my mill.

When I make a T-nut, I never tap them all of the way through. I use a spiral tap and only go about 80% of the way down. That way the studs stop before they touch the bottom of the slot. I have lots of factory-made T-nuts and they are built that way.

I never tighten them up enough to damage anything.

derekm
08-16-2010, 04:01 PM
1)With fixtures I always use a torque wrench. Too little can damage a table as well as too much. You might think you can tighten repeatably , so why not regularly recalibrate that arm of yours with a torque wrench.

2) Be careful with hardened/ high tensile studs. You may damage the table before you get enough stretch to clamp properly.

3)Make sure the T nut length/table strength. is matched the stud size and strength

gnm109
08-16-2010, 04:10 PM
1)With fixtures I always use a torque wrench. Too little can damage a table as well as too much. You might think you can tighten repeatably , so why not regularly recalibrate that arm of yours with a torque wrench.

2) Be careful with hardened/ high tensile studs. You may damage the table before you get enough stretch to clamp properly.

3)Make sure the T nut length/table strength. is matched the stud size and strength


I've seen tables with chunks pulled out of them.....