Gallery, Projects and General > The Design Shop
Mini Lathe T-slotted X-slide
andyf:
As to the depth of the lips, Peter, I suppose a lot depends on whether you propose clamping things as you might do on your mill, with the clamp bearing down on the workpiece at one end and on one of those stepped blocks at the other, with a piece of studding on the middle pulling up hard on the T slot lips. The lips on my mill are 8mm deep, but I still don't tighten up the clamp nuts too hard for fear of a breakage. When I got my baby Perris lathe (forerunner of the present-day Cowells), one of its cross-slide slots had a chunk broken out of it (the lips on that are about 4.5mm). The T nuts are only M6, so someone must have been really swinging on the spanner or Allen key.
Things are a lot better if you are simply bolting something down so the lips are sandwiched between the T nut and whatever is being bolted down, when over-tightening doesn't matter.
BTW, you mention a T slot faceplate. Mike made one of those, too:
http://mikesworkshop.weebly.com/tee-slot-face-plate.html
Andy
andyf:
A postscript:
At one of the Harrogate shows, I bought this for £10:
which was sold as a Unimat milling table, I think. It's about 77 x 105 x 13mm, so with some new holes in better places and corresponding tapped holes in the cross-slide, it would convert the latter to T slots if required, while retaining the original centre height when it wasn't needed. Maybe you could find something similar.
Andy
PeterE:
So, back at the keyboard after a short session in the workshop.
First some answers.
@John:
Thanks for the pic, very illustrative and I can se the mesh of tapped holes. Do you use any plugs in them or protect them in another way?
When thinking of making tapped holes instead of T-slots, I guess it would be useful to arrange them in rows at about the same way as a T-slot would have been milled.
@Andy:
Thanks for the info. I get the impression that the greatest "fear" among the readership is that the T-slot lips are too small and thus too easy to break.
You are right about my intended use of the T-slots. I intend to use them for attaching various kinds of equipment like a rear toolpost, possibly a milling slide, various sizes of angle plates, and last but not least, a dividing head. I think the X-slide will be too narrow to be a good boring table, and for that kind of work I have a small mill that can be used instead.
I picked up my copy of the Model Engineers Workshop Manual by GHT and re-read the section on T-slots and T-bolts. What I picked up was that GHT was very careful to use close-fitting T-nuts/T-bolts to make as much use of the lips as possible. This because the forces will result in a shearing motion rather than a bending motion on the lips. The shearing force is as I understand significantly higher compared with the bending force needed to break the lips. I tried to make an illustration to visualize it a bit.
Here the left T-slot uses an inferior T-nut, too small or soft in some way and the forces when tightening the bolt tend to bend the nut wings which in turn poses a major pressure at the edges of the lips with possible rupture as a result. The right figure aims to show a well-fitting T-nut nearly filling the slot which will result in a much better force direction, close to shearing only. In the latter case the strength of the slot can be used to its maximum.
Translated into ways of fitting, the following figure tries to show some general examples.
The first is the inferior T-nut/-bolt which should be avoided, the second shows a well-fitting one which is a much better solution, and the third aims to show how one can increase the strength by locking a longer bolt to the X-slide simply to save the T-slots in awkward setups. This also resembles bolting an angle plate or the like directly to the X-slide.
I hope you bear with me in spite of all my typing :doh:
Well, I am aiming to exchange the X-slide for something else. Apart from getting possible T-slots, I also want longer travel.
We will see where this goes, many other things have to be done before this one.
BR
/Peter
andyf:
Peter, those diagrams are instructive, showing that improvising with coachbolts etc is dangerous. I have made a few T nuts to supplement those which came with my clamping kit*, but I realise now they might benefit from a bit of further file work on their tops to ensure that only the outside edges are in contact with the lips of the slots.
* Speaking of clamping kits, :offtopic: why do all the studs come with a 1" or so plain unthreaded section in the middle? I get everything loosely assembled (which usually involves groping around on the floor to find one or two of the stepped blocks which have fallen off the mill table), and then find that I can't tighten everything up because the nuts run out of thread :bang: . I got so frustrated by this that I chopped a metre of M10 threaded bar into suitable lengths, and use that in preference to the studs which came with the kit.
Andy
PekkaNF:
--- Quote from: andyf on August 15, 2011, 07:15:45 PM ---* Speaking of clamping kits, :offtopic: why do all the studs come with a 1" or so plain unthreaded section in the middle? Andy
--- End quote ---
Better quality kits have these studs made such way that the short end thread will not pass trought the T-nut, bottom, jack-up, and eventually break T-slot, if used carelessly. That's why traditionally it's a stud and not a bolt. Some have this land only for looks apparently.....
Pekka
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