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making tee nuts

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Michael Gilligan27/11/2021 16:03:28
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Posted by SillyOldDuffer on 27/11/2021 13:02:20:

I suggest round headed t-nuts, such as coach bolts, should be used with caution. Tables are often made of cast-iron which is weak in tension. In consequence, they're rather easily broken, especially thinner lathe cross-slides.

In the diagram below, the bearing surface of a round nut (in red) is compared with that of a square T-nut (red AND green):

tnuts.jpg

When the round T-nut is tightened all the pressure is taken by the red area and increases the risk of breaking the table. The problem is exacerbated because the round form also concentrates stress at one point on the table. Conversely, a square T-nut increases the bearing area considerably and shares the bending stress along the slot.

[…]

 

.

Might I suggest that ‘caution’ would start with lopping bits off the circle, making the shape more like Journeyman's bar-stock version

The proportions of standard Coach Bolts [more strictly, it appears, Carriage Bolts] surely lend themselves to this.

**LINK**

https://www.westfieldfasteners.co.uk/cgi-bin/main2.pl?sub=Dy&page=Carriage_Bolts.html&tar1=Carriage_Bolts&tar2=,_Coach&imp2=,_Carriage

MichaelG.

Edited By Michael Gilligan on 27/11/2021 16:06:45

Bill Phinn27/11/2021 16:40:54
739 forum posts
103 photos
Posted by Michael Gilligan on 27/11/2021 16:03:28:

Might I suggest that ‘caution’ would start with lopping bits off the circle, making the shape more like Journeyman's bar-stock version. The proportions of standard Coach Bolts [more strictly, it appears, Carriage Bolts] surely lend themselves to this.

Two tee bolts of exactly this kind came with the tool kit supplied with my Warco milling machine. They don't seem to be available separately on Warco's site.

Nigel McBurney 127/11/2021 16:42:29
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in the good old days commercially made Tee nuts were case hardened steel and threaded Whit right through, never saw a new machine tool supplied complete with tee nuts, and it was a pity that the machine tool industry did not standardise on tee slot sizes, I made the nuts for my S7 out of round bar,they work well though must be made from a round bar of sufficient dia to give a decent flange. I have made Tee nuts from mild and tougher key steel with no problem .

Michael Gilligan27/11/2021 16:50:52
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Too late to edit my post, but … Here are the aforementioned proportions:

**LINK**

https://www.globalfastener.com/standards/detail_3252.html

MichaelG.

JasonB27/11/2021 17:01:52
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Posted by Nigel McBurney 1 on 27/11/2021 16:42:29:

in the good old days commercially made Tee nuts were case hardened steel

They still are even the imports, both the sets from Chronos and ARC that I have are hardened and it seems to go deeper than just case hardening.

JasonB27/11/2021 18:32:51
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As Michael points out unless you are using undersize coach bolts then the head dia is too big to fit into the "head" of the Tee.

Taking a typical 12mm slot and M10 stud the coach bolt has 80% the area of my Chronos Tee nuts and 87% of my ARC tee nuts which are a little shorter. So the slight loss is not really worth worrying about for our uses.

This shows the rounded head of a M10 coach screw with the footprint of the Chronos nut below, as you can see small loss of contact in the corners once the bolt head has been narrowed

t nut 1.jpg

Clive Foster27/11/2021 18:45:24
3105 forum posts
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I was told that "proper" industrial standard T nuts and similar tooling parts were hardened by heat treatment to reduce wear on the threads. So pretty much through hard.

Dunno how long or how many screw in and out sequences it takes to wear out a thread in softer steel as compared to hard steel but I'm pretty sure folk like us will never manage to wear the thread out of a soft steel T nut. Frankly I can't see me managing to lunch a light alloy one in my remaining active lifetime (I'm 67). If I did and couldn't be bothered to make a new one a Timesert thread repair would sort that PDQ. Timeserts are quite hard so if worried about wear you could fit them from the get-go.

Frankly I'd much rather take the risk of a worn out Tee nut in preference to misplaced swarf being ground into the Tee slot by a hard Tee nut. But I'm prejudiced having dug ground in swarf out of Tee slots but never suffered a worn out Tee nut.

Clive

Martin Kyte27/11/2021 18:58:44
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Personally I'd keep them soft. I'd rather bruise a T nut than a T slot.

regards Martin

Mark Rand27/11/2021 19:12:37
1239 forum posts
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When I first made a set for the Myford a couple of decades ago, I discovered that it was very easy to strip the threads due to the small slots leaving little meat on the nuts for the threads to live in. The next batch were case hardened and have given good service.

old mart27/11/2021 20:45:59
3724 forum posts
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I prefer to make the nuts longer than the bought ones by at least 50% and a much better fit in the slots. Some like to undercut the inside corner to make sure that there is no contact at the weakest part of the cast iron tee slot, only at the ends of the tee. I have used mild steel, stainless steel and aluminium for nuts.

Howard Lewis28/11/2021 07:12:02
6032 forum posts
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Doing a "quick and nasty" the nuts retaining my milling vice alignment "goalpost" are merely two tapped thick discs, with flats milled on them, filling the bottom of the T slot..

But this is an almost unstressed application, to hold the close fitting bottom of the pillars to the table.

For more heavily loaded applications, I make "proper" T nuts, ensuring that the top of the nut is below the surface of the table, to ensure that it does indeed clamp whatever is above it.

Within reason, the longer the T nut, the greater the area of table carrying the clamping load.

My Rear Toolpost on the lathe is clamped by a T nut extending the full length of the slot in the Cross Slide, with a stud at each end.

It is a good idea to peen, or centre punch the bottom threads to prevent the stud or bolt being able to pass through the nut and forcing it upwards. This should prevent the top of the slot being broken away.

Howard

Engine Builder28/11/2021 09:07:47
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I made some a while ago from hex stock that worked well.

An Other28/11/2021 13:47:53
258 forum posts
23 photos

As Jason points out above, very little difference in size between a modified coach bolt and a T-nut. Most coach bolts I have come across also have a short square section immediately under the head. I try to get bolts such that this square section fits in the 'neck' of the T-slot - simple enough to file it down if its slightly too big - this then helps takes the pressure off the head when tightening. This generally means that shank of the bolt is the same size or even bigger than any nut/stud which would fit in the T-slot. And the head of the coach-bolt is correspondingly large, so when the sides of the head are filed to fit in the T-slot, there is plenty of meat on left on the head, as per Jasons post above.

And how tight do you make these studs/bolts in use anyway?...never seen a machine damaged by a modified round-headed (actually near-elliptical) bolt pulling through the T-slot in more than 50 years of use.

I guess it is just as easy to overtighten a standard stud and T-nut, such that the stud goes through the nut, into the table, and 'jacks-up' the nut so it breaks the T-slot - and I would hazard a guess that there are far more studs/T-nuts in use than modified bolts, so I'll keep using my coach-bolts.

I have seen more damage done to machine tables by ham-fisted users driving the tool into them.

Michael Gilligan28/11/2021 18:58:50
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Posted by An Other on 28/11/2021 13:47:53:

[…]

Most coach bolts I have come across also have a short square section immediately under the head. I try to get bolts such that this square section fits in the 'neck' of the T-slot - simple enough to file it down if its slightly too big - this then helps …

… and [for the benefit of anyone who missed it] the link that I posted earlier tabulates the relevant DIN 603 2010 dimensions

27/11/2021 16:50:52

MichaelG.

john mostyn01/12/2021 08:12:44
8 forum posts
6 photos

Wow, thanks for the detailed replys everyone. The t nuts i need to make are 5mm ones for this mill slide. very small ones. Im also going to make some bigger clamps with some grooves in the centres to hold round stock as well.

cheers all

lathe mill slide

Michael Gilligan01/12/2021 09:06:15
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20108 forum posts
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[Assuming that you want/need Tee Nuts rather than the Tee Bolts that some of us have been discussing] :

First measure the slots in the table, and see what stock material will ‘contain’ the shape that you need.

MichaelG.

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