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How to use clamping kit on Atlas mill table

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JPMacG

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#1
I am using a clamping kit to hold work down to the table of my Atlas mill. By clamping kit I mean the usual kit that includes studs, flange nuts, Tee nuts and serrated blocks. I worry that if I tighten the nuts too much I might risk breaking out the table T slot.

What is the proper way to use one of these kits? Should I be compressing the T slot and not pulling up on the T slot? How would I do that?
 

VSAncona

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#2
On the better-quality kits, the threads of the T-nuts are swaged at the bottom. This prevents the studs from passing through the T-nut and breaking out the T-slot as you tighten the clamps down.
 

chips&more

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#3
That’s an interesting question. Never in all my years have I had that concern. I suppose it could happen, but I have never seen nor heard of that kinda damage to the mill table. However, on a similar note. When I got my second hand Bridgeport mill. I notice that the previous own(s) over tightened or used the wrong size “T” nuts and this caused a very nasty burr in the slot. This burr was so bad that I could not use guide pins or blocks in the 5/8” slot. I had to make a filling jig to carefully remove the burr. It’s all good now….Dave

Correction: I was only thinking milling table. I have seen many times, the “T” slot in a lathe compound or “T” slots in micro machines damaged/ ripped apart.
 
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RJSakowski

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#4
Typical use of the clamps will always have an upward force applied to the Tee nut and thus the casting immediately surrounding the Tee nut. It is conceivable that over-tightening the clamp could induce a fracture in the table. Without a specification for the table casting, it would be difficult to put a number on the proper torque. An improperly cut slot or the wrong size Tee nut could result in higher stresses on the casting.

After multiple decades, I have never had an incident with the clamps and I tend to be fairly aggressive when clamping. I would suggest starting out clamping with the minimum force required to secure the work. After a while you will get a feel for what is needed. Clamping should be done at three points, not in a line, if possible. This will reduce the amount of clamping force needed to properly secure the work.
 

woodchucker

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#5
On the better-quality kits, the threads of the T-nuts are swaged at the bottom. This prevents the studs from passing through the T-nut and breaking out the T-slot as you tighten the clamps down.
You can do that by taking a punch to the bottom of the tnut, put it in a vise upside down, then use the punch on the edge of the thread bottom and put a couple of dimples in the threads, it will make the thread stop
 

JimDawson

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#6
Where possible I try to secure the work to the table by putting everything in compression rather than putting the T-nut slots in tension in the conventional way. This is done by bolting through the work where possible.
upload_2017-4-3_9-14-22.png

This is not always possible of course, but I keep the T-nuts as close to the work as possible to try to minimize the tension on the T-slot.
upload_2017-4-3_9-14-56.png
 

JPMacG

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#7
Thanks everyone. When I purchased my MFC several years ago I got a basket of extra MFC parts along with the good mill. Among the parts was a table with a broken out slot. I don't know how it happened, but I want to be sure that I don't do the same to my good table. It sounds like there should not a problem as long as I don't use my 24 inch breaker bar on it.
 

RJSakowski

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#8
Also, it's a good practice to keep the stud as as close to the work to maximize the clamping force. The force applied by the stud is divided between the work and the step block, the ratio being the ratio of their respective distances from the stud.
 

wa5cab

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#9
Don't use a bolt in a T-Nut without confirming that the bolt isn't too long. And to repeat what was written back up the thread, don't let the stud run through the nut.
 

bfd

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#10
if you want to make sure your part doesn't move put a piece of paper under the part you are clamping the abrasiveness of the paper will help stop the part from turning or moving. then just tighten normally with a standard length wrench . bill
 

Silverbullet

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#12
On a mill of the atlas size nothing more the twenty ft pounds is plenty. With two clamps that's 40 ft pounds of holding down pressure. Heads on Mower engines only use that and there constant heat and cooling they stay tight .
 

Bi11Hudson

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#13
On my Atlas (MFC), I use 3/8-16 bolts with a square head. I have several lengths that I acquired from a now out of business supply house. They have eliminated the punch-through (worry) problem. But still I worry about the "pull-through" aspect of clamping. For the same reason you asked... These are ungraded black iron(unfinished steel), not good grade 5 capscrews. And I watch older machinery for more of different sizes for use on other stuff. They fit the slot very well and I use the clamps and nuts from a clamping kit.

I usually torque to "one snap and a grunt", as opposed to "3 snaps and a grunt" for automotive and mill work. Not much good with real numbers and torque wrenches, unless I'm doing something critical like head work on an automotive engine.

I have have noticed that as I age, that "3 snaps and a grunt" goes more toward the high tolerence of a torque wrench.
 

wa5cab

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#14
I'll point out that a square head bolt is more likely to break out the T-slot than is a properly fitting T-nut. It will have less surface area in contact with the upper surface of the slot. The only plus about it is that there is no possibility of screwing the stud down hard against the bottom of the slot. Which can damage even a steel table.
 

Round in circles

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#15
Don't use a bolt in a T-Nut without confirming that the bolt isn't too long. And to repeat what was written back up the thread, don't let the stud run through the nut.
May I add ?
Don't use a square shouldered timber coach bolt upside down in the Tee slot either, it will try & rip through the slots , use proper " Tee" nuts that have a quality fit across the slot & depth of the slot and are at least three times the length of the slots width .
 
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Rob

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#16

wa5cab

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#17
Unfortunately, some square head bolts that I've seen in recent years have washer faces. Meaning that the corners of the square aren't actually in contact with the bottom of the slot. The same note is on Page 8 (printed page #) of MMB-5. But for once, I would not do it. Buy proper T-nuts and thin them down to 7/32" instead. And if necessary, grind the sides a little so that they will be a slip fit in the slot. You only need to make a few of them, and they should last forever.
 

Rob

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#19
Unfortunately, some square head bolts that I've seen in recent years have washer faces. Meaning that the corners of the square aren't actually in contact with the bottom of the slot. The same note is on Page 8 (printed page #) of MMB-5. But for once, I would not do it. Buy proper T-nuts and thin them down to 7/32" instead. And if necessary, grind the sides a little so that they will be a slip fit in the slot. You only need to make a few of them, and they should last forever.
After I read this I had to go and check the 3/8" bolts that I had turned down the heads on. Luckily all mine where flat and do not have a washer face. I have several short ones that I use but I use them to hold something that has a hole in it. A couple of them are jigs that I made to hold something else.
 

wa5cab

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#20
Yes, it appears that the washer face is uncommon.
 
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