Thread: Sieg C3 backlash problem
I've just done an introductory thread over here: [ame="http://www.mycncuk.com/forums/showthread.php?p=8058#post8058"]New member from the IOM - MYCNCUK[/ame]
So I thought I would start one here to try and get help with a problem with my minilathe.
It's a Sieg C3 and the main problem I have is as follows.
I recently bought the Sieg DRO conversion for the lathe, and fitted it a few days ago.
It's a nice little setup, although it wasn't quite a straightforward fit as some of the bits didn't fit together out of the box!
That's all done now, but the big problem is a lot of play/backlash that has appeared since fitting them. NB - nothing I've 'adjusted' to get it to fit together would have been responsible for this.
Where it suffers most is on the cross slide. If I grip the cross slide and push the assembly above it (compound/toolpost etc) in & out (ie towards the back & front of the machine across the bed) it will move by something like 0.5-0.75mm! Surely there shouldn't be any play that you can feel by hand?
The compound also suffers from this but not quite as much. Still enough to be a nuisance and I would describe it as excessive even though I have nothing to compare it to.
I haven't tested the lathe on any project material since fitting these, but I'm guessing I'll get tons of tool chatter and will get horrible finish & be restricted to very shallow cuts etc as a result.
Before fitting the kit there was a little bit of play like this in the cross slide but a fraction of what is there now. Am very disappointed indeed at this stage but I'm hopeful that the problem can be resolved.
The gibs seem to be adjusted fairly well as both slides move quite freely without any significant wobble if you try to twist them by hand, so I'm not sure what else might influence the correct fit of this kit, ie what I can do to tighten it all up so it operates smoothly and rigidly.
All ideas gratefully received!
What other measures can I take to make the lathe as play/backlash free as possible? I already lapped the gibs to smooth the surfaces and that helped a little, and I've now bought some brass gibs (not yet fitted). Looking at them they seem to have one sharper edge and one more rounded edge (opposite side of the profile) to them so I'm uncertain which way round would be best.
I know I can also get better bearings for the lathe but I'm not sure how much difference they might make, or what else will make the most difference to its accuracy/rigidity.
Apologies if I've posted this in the wrong place, and I look forward to any useful suggestions you folks might be able to give me to sort out this problem.
I'm itching to get using it again but I suspect it will be horrible to use at present with these issues.
Can you outline what was involved in fitting the DRO... or what was taken apart to fit it? I dont know the C3 but I have a similar movement in my ancient lathes and this is simply wear on the nut. What I did find was stripping them down and rebuilding them had a big effect until I discovered that the nut wears differentially and was reversible... accidentally refitting it back to front increased the backlash by 2mm!
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.
Any chance you could replace the bushes and collar with a couple of ball races?
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.
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.
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 # ]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.John S -
Yep - you're right about that John but I can't see any feasible way of adjusting the endfloat I have. Sure you adjust where the allen bolts tighten up slightly to account for the screw being slightly off axis or whatever you might call it, but I don't think you can adjust the problem mine has without adding shims.
I did get instructions with my kit but nothing of any use to help with this issue.
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