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T-Slot Size vs Clamp Size?

whydontu

whydontu

I Tried, It Broke
Premium Member
Maybe a silly question. My new mill has 5/8” tee slots, all of the 5/8” tee nuts I can find are 1/2”-13 thread. All of my existing tooling, vises, and clamping hardware are for 3/8”-16 thread. My millling vise base won’t fit 1/2” bolts.

Any reason I shouldn’t just make some tee nuts to match the 5/8” slot dimension, but tapped 3/8”-16? Then I could use my existing gear and not have to spend $$$$ on new workholding stuff.
 
First project on all my mills was to make proper fitting T-nuts, with a range of bolt sizes. I have 3 mills and a radial arm drill that have “5/8” T-slots” - every one is a bit different (that is why the clamp kits fit so poorly, they have to fit quite a range of table sizes).

I don’t like the fit of the generic clamping kits’ T-nuts (one sign of an abused machine is that the slot grooves are dented from over tightening poorly fitting nuts/bolts). A good fitting nut, 50% longer than the generic ones reduce wear/damage to the table and can safely be snugged (and deep enough to thread in a decent bolt) - of course one doesn’t run the tap right through so as to protect your table.

so yes, make a set of T-nuts.

On your vise consider making some nice T-bolts, use a 1/2” thread, but neck the portion where the vise flange is (then it is the same wrench size as the clamp set bolting) - leave as much bolt in play as possible. In my shop, every vise has its’ own hold down bolts. In my case, this allowed me to go up to 5/8” bolting (just fits) - where you can, make things as robust as possible.
 
Just make sure you put a heavy stake(s) on the bottom of the t-nut to prevent the bolt from protruding below the bottom of the nut, or as @Chipper5783 mentioned, don't tap completely through.
 
Lots has been said on this forum about the risk of broken table TSlots caused by using unstaked or tapped through nuts or unsupported clamps. If you can, use long T-Nuts and make them as wide as the bottom of the slot allows. Try hard to avoid non-compressive applications.

Keep in mind that the torque required to properly clamp parts with T-Nuts and bolts is WAY WAY WAY lower than their tensile strength.

I know you know all that, but who knows who else is reading this.

I have at least 6 different sizes of T-slots in my shop -maybe more. So I have lots of places where I've made custom T-Nuts and custom bolts.

So ya, use what fits, but always strive for columnar compressive clamping, and never allow the end of the bolt to reach the bottom of the T-Slots.
 
Mcgyver said:
Good reminder ...... my commercial ones all seem to be tapped through ..... keep thinking I should put a spot of weld on the bottom corner then grind off any that is proud of the bottom.
Click to expand...
I give them a heavy staking (couple locations) with a center punch - only takes a couple minutes to stake all the T-nuts in a clamp kit - could save a world of hurt later. Another option is a suitable size ball bearing, give it a good whack or squeeze - looks good and distorts that bottom thread to prevent a stud/bolt threading through.
 
Chipper5783 said:
I give them a heavy staking (couple locations) with a center punch
Click to expand...

I've tried that but found they are tough stuff so don't deform easily and its a somewhat loose thread fit. I haven't done it yet, but like the idea that a small dollop of weld makes for a more positive stop given they get a fair bit of torque (not too hard to torque through punch marks.)
 
1) My purchased (as part of the clamping set and handful of extras) 7/16” T-Slot Nuts aren’t tap all the way through and I do the same with the ones I make.

2) I made nuts that have both 1/4-20 & 10-32 tapped holes for using my smaller toe clamps on the mill table.

3) As an expediency, I have made 1/4-20 & 10-32 T-Slot Nuts by using EZ-Loc inserts in standard nuts, staking the bottom of the inserts with a small cold chisel.
 
IMO - custom & tightly fitting T-nuts is a simple and very beneficial upgrade to standard (one size fits all) T-nuts.
I make them with max width that will fit the mill slot and also the max length that I can get to slip in.
I also make them to look more like a U-nuts rather than T-nuts so that the load is spread further appart. This concept was discussed 6 months ago in the link below, see post #8.

Chipper5783 said:
option is a suitable size ball bearing, give it a good whack or squeeze - looks good and distorts that bottom thread to prevent a stud/bolt threading through
Click to expand...
I have lots of ball peen hammers - I use a small one, with the ball side down on the threads to be deformed (staked). Then give it a solid hit with a much larger hammer. (Works like using a steel ball but without the ball getting shot out sideways.)


canadianhobbymetalworkers.com

Tips/Techniques - Mill hold downs

Cool video, no loud music just the sweet sound of milling and drilling!
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Revision to above link - If the T-nut (or U-nut) is not confined and tear-out is a possibility, then max torque on the bolt is 10 to 12 ft-lb. In this situation multiple clamps are used.
 
Last edited:
CWret said:
I have lots of ball peen hammers - I use a small one, with the ball side down on the threads to be deformed (staked). Then give it a solid hit with a much larger hammer. (Works like using a steel ball but without the ball getting shot out sideways.)
Click to expand...
I have also used upside-down ball peen hammers to gently stake rivets, etc., but always use a brass or copper hammer as the "beater:" two hammer faces hitting each other can cause them to chip.
 
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