Member postings for John Haine

How about making the manuals open-source? Then all the users can contribute to them as they learn the niceties of the machines. There's no great incntive for Ketan to produce a good manual, but plenty for the users or prospective users.

I used to make model plane fuel tanks from brass shim, cut with scissors, soldered using Ersin Multicore electronics solder, no problem at all. Probably I polished the brass with a bit of brillo and washed it clean if it wasn't bright - this was a long time ago (getting on for 50 years I realise with a shudder). No need for any additional flux. Modern electronics solder is lead-free, needs a rather higher temperature, I find that it is also fine for soldering for example brass and steel together using some white paste non-acid plumbing flux bought from a local plumbers supplier.

Just for the record, if there is a 127 tooth wheel in the train and an inch leadscrew, the theoretical error can be zero as 1 inch is defined as 25.40 mm. 127 is 254 divided by 2, so you can set up the exact ratio needed for a metric thread defined as a pitch that is a rational number in mm, given enough changewheels.

Steve, an interesting idea. Actually, you don't even need to feed all the phase inputs, just one, though at high powers the input diodes might suffer.

OK, so yesterday I ordered a Z-section Powertwist belt from RS Components, it arrived on my desk this morning, just fitted it and tried it out on the piece of 1.5" MS bar that was defeating me before and there was no problem whatever. I parted it off running at lowest open speed (210 rpm) with auto feed applied at about 5 mm/min by the CNC, no sign of slipping or anything other untoward. Back up and rnning again.

The lesson is that for the newer Myford 7s you need to buy the Z section belt for the c/shaft to mandrell drive, not the A section which the older lathes used. Glad to say that RDG have offered to refund the cost of the unsuitable belt and hopefully will update their website.

John.

I've now ordered a Z section Powertwist belt from RS. For the record, the big-bore Myford has a Z section pulley on the C/S to spindle drive, whereas the older Myfords had A section. This is obviously why the belt from RDG is no good, it's too big for the pulleys. You would think they might be aware of this now they own Myford wouldn't you?

Thanks Nick. Well, that seems clear then, measuring the width of the top of the vee groove on the pulley it is very slightly under 10 mm so it is unlikely that the 13mm belt that RDG sell as suitable for Myford is actually suitable for the newer big bore S7. Actually looking closely you can see the belt virtually riding on top of the pulley rims, so there is very little actual surface area to give friction and therefore drive. Lathes.co.uk also quote A-section for the h/s drive belt but on the newer lathe it should be Z-section it would seem. Bricky seems to have had problems with z-section Powertwist so I'm inclined to try the more expensive T-link, still cheaper than getting the service engineers out and worth a try as an alternative to dismantling the headstock for an endless belt. As they say, when you're up to your a***e in alligators it can be hard to remember you set out to drain the swamp!

Thanks Francis, but now I'm really confused! I also have the big bore machine, I assume that you are talking about the belt from C/shaft to mandrel? I've noticed that the belt that I have looks rather wide for the pulley groove - it is about 12.9 mm. So is that right, the groove width on the big bore machine is narrower than on the older ones? I see that Z size is 10 mm and A size 13 mm. I could get Z size in either PowerTwist or T-Link from RS, did you try the Powertwist Z size please?

John.

I have a metric super 7. The X-slide and topslide have 2 mm pitch feedscrews. The T/S has a barrel with a mm scale. As I found out to my cost one day, the leadscrew is still 8 tpi! 8 tpi is 3.175 mm, so the scale on the handwheel is calibrated in mm up to nearly 3.2 then goes back to zero! As it doesn't have a zero-settable thimble the graduation is next to useless. Even if it did it would only be useful up to 3.175 mm.

For metric screwcutting, Myford provide tables of approximate ratios that are good for some common metric threads which are just fine for shortish fasteners but obviously if you want to make a metric measuring screw they aren't and you need a 127 tooth change gear (which can only be fitted with some difficulty). However since almost all the threads we cut are for fastening the approximations are not a problem since the errors are almost certainly less than the machine accuracy anyway.

I have converted to CNC so the imperial L/S isn't an issue, it's all sorted out in the software.

J.

Thanks for the comments.

Kwil, it's not that I'm diffident (if I was I wouldn't have taken a cutter to the original V belt!) just that I'm hacked off that what I bought in good faith hasn't delivered.

This isn't a Fenner belt but the cheap equivalent and yes, it is plastic-y. I have tried it both ways round but it makes little difference.

Bill, I guess you have fitted the belt on the motor-countershaft? Mine is on the C/S - H/S mandrel. On the S7 the M-C belt isa poly-vee anyway. The problem I get is that even if I put the lathe in back gear, the work doesn't go fast enough for the tool to cut properly so it digs in and jams the mandrel. With the belt on the motor to countershaft I guess you get an extra stage of reduction...

Oh well, I guess I'll need to buy the expensive Gates product..thanks for your replies. Is there anyone who can confirm that the Gates product really does the business please?

Last MEX I bought a link belt for my Myford S7 having read that they gave smoother running and less vibration, from a well-known ME supplier. So with slight trepidation I cut through the original Vee belt and fitted the new one, and I have to say that I'm extremely disappointed! Normal running is OK though not noticeably better, but now I CANNOT part off - the belt just keeps slipping even though I have it as tight as I can get it.

Yes, I have cleaned the pulleys, but it makes no difference. Actually even when I tighten the belt it doesn't make much difference. Parting used to be trouble-free but now effectively I can't do it at all.

Does anyone else have any experience of these please? I bought the one I did because it was a third of the price of the "Powertwist" belt sold by Tony at Lathes.co.uk, maybe I can see now why it's only a third the price! Can anyone give a positive (or negative) recommendation for the Powertwist belts please? I'm reluctant to fork out 30 quid + for another link belt unless I know it'll work, but I really really don't want to have to dismantle the headstock to fit a normal belt!

John.

The company referred to above by Russell is Renishaw plc - bit of an unsung hero of Britich engineering IMHO - worth browing their website. The touch-trigger probe was their first product, the first device to allow a CNC machine to automatically orient itself relative to the workpiece I believe. It was patented internationally, e.g. US 5146691.

There have been a couple of home-made interpretations, e.g.

**LINK**

and a recent one in the Digital Machinist mag.