GH Thomas S7 topslide improvements

Just finished 'the' GH Thomas S7 topslide improvements - pinning the gib and adding a little thumb-operated topslide lock. These seem useful, and good motivation to generally strip, clean and pander to the assembly.

I actually bought a complete, 'ugly' S7 topslide from the Bay of Fleas a couple of years ago, intending to try this out without affecting my original. This was prescient, as I promptly broke the original base casting and swapped it out for the newly-acquired. The tapered stub had evidently been cracked by a bit of excess 'nipping' while the left and right pressure pads had been reversed, causing the tips to dig in and induce the crack. But the topslide itself had been sitting in a drawer since.

But nothing is thrown out around here, and that broken base became the answer to clamping the topslide while drilling for the gib pin, after the broken stub was machined-off - this is the bit where GHT talks obliquely about 'clamping it as best as you can'.

The only other thing I varied from the GHT instruction was that rather than fiddle with the screw to work out where to position the thumb turn, I simply fixed it in place before trying it. I then filed down the finished tip to get it in order. The thread pitch of 2BA is about 32 thou in old money, so it wont be much - but do ensure that the leading tip is a 'full' 1/8" at the kickoff.

That ugly topslide was then cosmetically improved by rebuilding the corner collision marks with J-B Weld. And a layer smeared on the mounting surface, before being 'just' faced off with a flycutter and painted with Paragon enamel. Finally, new gibscrews added and the whole assembled on the bench.

The other thing I tried is the thin white line you might see between the end plate and the screw index dial. I added two PTFE wafers, cut from 0.5mm sheet with wad punches. I have previously ripped thicker washers from a piece of bar, but they seemed a bit clunky.

Anyway, now done. And it all feels jolly nice to use.

Cheers, Colin

Edited By Hillclimber on 25/10/2021 11:38:34

Nice job. Must do that myself.

You may find an article on Woody's Workshop website on incorporating roller thrust bearings into the top and cross slide feedscrews interesting.

Rod

A very neat job Colin.

I also have carried out GHT's slide gib pinning and locking screw mod to my two Boxford CSBs and my Myford ML7 so I know what you meant when you said:-

- this is the bit where GHT talks obliquely about 'clamping it as best as you can'.

Regards

Dave

Yes very useful done mine some years back

H

I did the top slide clamp by GHT years ago, well worthwhile, in fact anything by GHT is worth making.

I converted my non power crossslide myford S7 last year following his guidance, so much better than the original friction dials.

Regards

Derek

Rod, thanks.

Tell you what though, I bet I can cut two PTFE wafers quicker than many could say 'roller thrust bearing'....

Cheers, Colin

Isn't PTFE rather too compressable for that particular application. ?

regards Martin

Any loading will be unidirectional with the topslide set normally, right? So we only need to consider each of the wafers, which are respectively about 20 thou of an inch with a surface area of about 0.4 sq inch.

I have not sought to calculate the axial load on the cutting tool, which will be transmitted directly through the wafer. But at that thickness (thinness?) and load area, it does not seem to me that it would be going very far? I certainly see this stuff being used for high-load applications, albeit that I am using what I assume to be a virgin PTFE.

But other thoughts are welcome....?

Cheers, Colin

I did mine many years ago and I agree, for the time taken is definitely worthwhile. Also did his modifications to the cross slide collar and added the quick retracting topslide. The later makes screw cutting so much faster. The larger graduated collars and the locking arrangement are much superior to the original Myford system. The larger collars are much easier to read (particularly the topslide ) and can be reset with no risk of moving the slides. Although considerably more work I highly recommend them.

John

Yes John, done mine a few years back now and reall can’t imagine life without the mods and as you say screwcutting is a doddle.

John, I can only express the deepest envy at the quality of your work here. The micrometer dials are gorgeous, and beyond my capacity and experience.The problem, as always, is time. I am trying to press on and deliver some essentials to allow me to do the 'real' projects I have. And even affording me the luxury of the minor work I undertake on my lathe is at the expense of other metal-bashing. Although I dont ever regret it when I do.

I did install one of Steamer's resettable leadscrew dials and love it. And just wish that someone was manufacturing other items such as the gearbox and dial for GHT's retractible topslide. But I guess that the designs may still be tied up somewhere by copyright restrictions?

Cheers, Colin