Mini Lathe T-slotted X-slide

[PeterE]

Ever since reading the Mini-Lathe start pages in MEW I have been thinking about how to get a T-slotted X-slide. It seems like a very useful item and having seen how many work tasks that are simplified and/or possible just by utilizing the X-slide, it is almost becoming a must as a mod.

The main problem is the balance between swing over X-slide vs thick enough X-slide to harbor small/large enough T-slots.

The item for comparison will obviously be the Myford which have the same center height (90 mm) as the Mini-Lathe. The main difference here is that the Myford X-slide is 125 mm (5") wide compared with the Mini-Lathes 68/70 mm. The larger footprint is of course an advantage, but if the small Unimat machines can have a T-slotted X-slide, why can't a Mini-Lathe have one?

Having thought long and hard, I have reached the first sketch-like drawing which I attach below.



It shows the outline of what I am thinking of (please do not trust all the measures yet - they are in some cases just copies to be adjusted and therefore wrong!)

I am aiming for about 200 mm in length (suits a slice of 200 mm square CI from CES) and I will make it 70 mm wide instead of currently 68 mm. My main issue has been how much material shall be left untouched between dovetail and T-slots to maintain proper strength of the whole slide??? As calculated now the slide is set to 20 mm thickness giving 5 mm untouched material in the center which I hope will be enough.

The original X-slide is 16 mm thick so I will lessen the swing over X-slide with 4 mm from 57.5 to 53.5 mm, something I certainly can live with.

The T-slots have the same height as the Myford slots which seems to be strong enough since there have been nearly no comments on them that I can find. The difference is that I standardize on 8 mm T-slots for all my machines and hamemade tooling so the slots are 2 mm narrower than the Myford.



So, my question to you knowledgeable people on the forum is; Have I done any major errors in my design or is there anything else that I may have missed??? I know this question has been up on the ME-forum but I felt I should ask here as well so I hope you don't mind.

BR

/Peter

[mklotz]

Have you given any thought to an array of tapped holes in lieu of T-slots?  Tapped holes would offer almost as much clamping flexibility and might be sturdier than thin-lipped T-slots.

Just a thought.

[andyf]

Here's a fabricated one, Peter http://mikesworkshop.weebly.com/tee-slot-cross-slide.html .

Mike, who made it, is a member of the ME forum, so if you posted there he may already have referred you to it. I've seen his mini-lathe, and the cross-slide certainly looks the business.

I suppose the maximum diameter you can turn will reduce slightly with any design of tee slotted cross-slide, but turning 7" diameter is probably a big ask for a mini-lathe.

I'm on the lookout for a Myford cross-slide, because one can be fitted to my non-Sieg/Real Bull 7x12 lathe, as shown halfway down this page: http://andysmachines.weebly.com/steves-improvements.html

Andy

[PeterE]

Hi Marv and Andy,

Yes, I have thought of using a pattern of tapped holes, but perhaps discarded the idea a little too quickly.

What I think is the biggest risk with tapped holes is that they offer too big a chance for swarf and other debris to get below the X-slide and into the slideways which then will be difficult to keep properly clean. Of course some sort of plug would solve that quite easily.

Hmmm, some more thought on this is needed I think 

Then about the thin-lipped T-slots. I have tried to find as much info as possible on that particular subject, but have not found much. One thing though is that there is a great difference in force if the pull on the T-slot lip is unsupported (bending) compared with supported (shearing). the only thing making me think about thin-lipped T-slots is that the Myford T-slots are thin-lipped and have "survived" through so many years to date. Other than that I really do not know. 

Looking at the boring table of my X1L mill, the table is much thicker (+10 mm compared with my sketch) giving the T-slots more material on the lip (measured to 8 mm).

Then I just had to measure the T-slot on my Unimat clone as well, and that T-slot is also an 8 mm slot with the same measurements as I have planned for a new slide. That makes two major machines going for thin-lipped T-slots! 

@Andy; Yes I posted at the ME forum (the post was a bit different though but the subject the same) and got some valuable comments there as well. Sounds good to hear that Mike C's design works well. That makes one tick for T-slots.

7" diameter might actually be attempted as I have had thought on making a new faceplate with T-slots (well here they are again  ) instead of drilled through slots as the spindle fastening method "steals" much of the clamping facilities.

Oh, I need to think a bit more on this before deciding the way to go. My "major" is in electronics and nowadays I am only working with computers and information, thus having little knowledge in mechanical dimensioning. So, being careful and wanting to do it right, I sometimes get a little lost as you perhaps can see (read).

All input is most valuable!

BR

/Peter

[doubleboost]

I used to own a axminster bv lathe i drilled and tapped the x slide in a pattern of 8 mill holes did the job great
This is the only picture i can find

John

[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 


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,  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  . 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]

* Speaking of clamping kits,  why do all the studs come with a 1" or so plain unthreaded section in the middle? Andy

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

[dickda1]

Check out this page:

http://www.statecollegecentral.com/metallathe/A-11.html

I have bought castings from this guy before - good quality grey iron.  Costs an arm and a leg to ship.

-Dick

[PeterE]

Hi,

@Andy;
Something in the back of my head says "don't overdo the filing"! I guess that creating a pronounced "edge" bearing on the inner underside of the T-slot lip may create a not so desireable force pattern. I cannot say why, but it feels like the best is to get as close to a wide spread load surface as it also would provide a a good grip from sliding.

I understand your comments on the studs, mine are the like. As pekkaNF says, there was a purpose which I did not catch before - thank you for explaining that Pekka! 

Then I guess that the inch of unthreaded land could well be lessened to about 10 mm (3/8") to give more usable thread above the T-slot. Will think of doing that when I need more T-slot studs.

@Dick;
Thanks for the link! Yes I would imagine that the shipping costs will be high. I found much the same but for a Boxford (same as the other one on the mentioned site) available from Lathes in the UK which is closer to me in the west of Sweden. Both castings seems to be 1 1/4" or 32 mm thick, and they are a good deal wider than teh Mini-lathe can use so there will be too much scrap I think. Have been thinking of buying a 30 mm slice of 200x200 mm cast iron bar from CES instead.

Have to think about that 

BR

/Peter

[PekkaNF]

I understand your comments on the studs, mine are the like. As pekkaNF says, there was a purpose which I did not catch before - thank you for explaining that Pekka!  /Peter

I got nice assortement of studs from local "nuts and bolts" shop. They were of better quality and greater grade than allthread (which I bought couple of bars as well next to nothing). Only thing to check is the length of the "short" end, but all short ones were spot on. Sometimes even I get lucy.

Pekka

[PeterE]

Good to hear that there still are shops that can sell useful stuff like these studs, and I hope your luck continues Pekka!

BR

/Peter