Sieg C3 backlash problem

[irving2008]

Sorry for the slow reply!

I've found the source of the problem and sorted it (at least for now).

It wasn't anything to do with the nut, but related to a collar on the cross slide screw. I forget the name of the part but there's a fitting that goes on the end of the cross slide which keeps the screw locked in place.
Between the new screw and new piece to hold it on (which has a recess that the screw collar goes into) there was over 40thou of a gap which meant you could just pull the slide in & out by this amount. In comparison the original parts had approx 11thou of movement, which wasn't too bad.

I'm disappointed that an 'upgrade' kit made by Sieg for this very mchine would make it worse. I know you can work around backlash on a manual machine but ultimately you shouldn't have new parts from the same people making it a more sloppy machine! Eventually I want to convert to CNC and things like this are a backward step.

I emailed Sieg & got no reply, although I believe they forwarded the message to Arc Euro. They replied to me but they seem to have misinterpreted my gripe into a complaint that the kit should make the machine more accurate. That's not the case, as I've just tried to convey that I don't think it's acceptable that a kit to improve the use of the machine should introduce such a large amount of slop.

I've not got round to replying to them again yet. They did offer a refund if I'm not happy but that's never been my intention. I think they have indeed made an effort to answer my questions but not quite from the right perspective.

Anyway, I've managed to make a plastic shim which fitted perfectly so it solves the problem for now, but obviously that will wear.....

If I get updates on the stance on this I'll pass the info on. My opinion (as a relatively inexperienced machinist) is that it's a sub standard product to have such a poor fit over the original parts even though I like it a lot. Others may well disagree with that.

Cheers
Jim

Ah right, so what you found was the new collar increased the end-float in the screw. Is there no adjustment to take up the endfloat?

On older lathes the endfloat was 'controlled' by a collar, or more often the handle itself, and shim washers under its fixing bolt. Newer lathes often have a thrust bearing and a screw on cap to adjust the pre-load and remove the end-float.

[Cret]

No such luck unfortunately.

Sorry yes though, it's end float of course! I should know by now from messing with car engines & cranks etc.

So the end float is about 42 thou, with no means of adjusting this unless you make shims yourself and that's not easy for me to do, because the collar only has a slightly bigger diameter than the screw shaft itself, so it's like a washer but with a small difference between the hole diameter and the outside diameter.

As it happened I began measuring various things to find a suitable shim source, and found some clear plastic packaging for Woolies dust masks of all things. 35 thou thickness precisely - perfect, and easy to cut with scissors, just I doubt it will last all that long.

I've kept the rest of it so I can make more if need be in future.

I would LOVE to fit some sort of thrust bearing or ball race but I'm no way confident enough about machining out the recess to fit something just right. I'm too inexperienced not to balls it up!

Here are some pics to show what's what:

Old collar thickness:


Old recess depth:


New collar thickness:


New recess depth:


As you can see from the numbers that gives a relatively huge increase in endfloat, and I think that's really poor. Like I've said, yes you can learn to work around backlash and probably should do as a skill to learn, but it's not the point. You don't buy parts to improve a machine and have them make a particular tolerance of it 4 times worse!

Can you imagine if you bought a new porsche*, then bought a sports upgrade package from the porsche dealer that made it worse? I doubt you'd be happy to accept it and I don't see why this should be any different. I'm not sending it back since I've fixed it, but I think Sieg ought to either machine it with a better tolerance, or else supply a shim package or a bearing with it.

*Arbitrary car since I'll never have the money to buy one and would probably get something else anyway.

[John S]

I have fitted these kits in the past and I'm sure they are adjustable.
I think I may still have the bits to one kicking around because I bought a C3 two years ago but seem to have misplaced it somewhere.

Last I saw it was still in a big wooden packing case but can't recall seeing it lately [ note to self - check Tardis No 2 # ]

[irving2008]

I have fitted these kits in the past and I'm sure they are adjustable.
I think I may still have the bits to one kicking around because I bought a C3 two years ago but seem to have misplaced it somewhere.

Last I saw it was still in a big wooden packing case but can't recall seeing it lately [ note to self - check Tardis No 2 # ]

If that was the case John (not saying you're wrong btw), wouldn't the instructions have mentioned it somewhere?

[John S]

Don't recall seeing any instructions, mind you when I find the bits they will have been kicking around for so long that if there were any they would have gone walkabout.

I have fitted these to a few things and can't remember having problems but then again i may have adjusted any play out.

I fitted a set to a Taig mill, they go nearly straight on because these things work on 20tpi screws.
They are just an encoder that counts based on 20.