SC3 chuck out of balance

Hi,

I am the proud owner of a new Super C3 Lathe. Having been a mechanic in the R.A.F. and with out local council for the last 25 years now happily retired), I am no stranger to the trials and tribulations of 'gremlins' and 'sod's law'. I'm very happy with the new lathe but it has one trick up its sleeve that I would be grateful of a solution to.

When running under no load at 50 to 900 rpm it seems fine, but at around 920 to 1000 rpm it developes a vibration, it peaks at 940/950 rpm. After that it appears okay. I'm guessing that it is the chuck that is causing the problem. Is there any way of balancing it? Either by adding or removing weight to it. Also, is this a known problem?

As you may gather, this is my first lathe and the mechanic in me wants to know the ins and outs of its workings!

Many thanks, Colin.

Hi Colin

First of all welcome to the forum. I suspect that the imbalance you are noticing is caused by the fact that the back plate is drilled to accept both the 3 jaw self centering and and 4 jaw independent chucks. The 3 jaw have 3 mounting studs and the 4 jaw have 4 mounting studs and the spacing means that the back plate is not balanced correctly which becomes more apparent at higher revs.

I think some people have suggested that it may be possible to put blanking plugs into the vacant holes but securing them so they don't fly out may prove challenging.

If you look on the ARC site there are links to various articles and sites that cover the Super C3.

Enjoy your new toy

Regards

Martin

PS

A bit more information from the ARC site . If you look at Fig 33 you can see how the mounting holes are distributed on the back plate and how this can cause a certain amount of vibration. Most of the small lathes that have bolt on chucks have this arrangement of holes so it is not unique to the C3 lathe. I have a DB7V from Chester and this has the same mounting arrangement as do similar lathes from the likes of Warco, Axminster etc.

Edited By Martin W on 04/11/2015 17:07:49

Colin I would suggest that you talk to Ketan at ArcEuro. If you are in the UK and close to the East Midlands then perhaps pop in and see him. HTH.

I had no problem when using the 80 mm chuck on the lathe but when I updated to the 100 mm chuck and backplate I had this problem. The back plate is thick and drilled for both three and four jaw chucks so there is an imbalance due to the non symettric arrangment of holes. This led to vibration in the same speed range that you cite. At a later stage I upgraded my machine to a spindle with a 100 mm flange (as used on the Real Bull lathes) This eliminated the vibration.

Mike

I'm struggling with this I have to admit. If two hole patterns which are individually balanced are superimposed, as long as no two holes are one, intuitively you'd think the superimposition would also be balanced. Another way to think about it is to imagine the plugs of material you take out in their relative locations. Again, if they retain those locations the 3 plugs pattern and the 4 plugs pattern would be individually balanced and if superimposed you would thing the whole would also be balanced as long as no two plugs overlap. If the whole plug pattern is balanced you'd think that what it leaves behind would be also. This is making my brain hurt...

John

If you look at the figure 33 on the ARC site I referred to above you will see that the holes are not uniformly spaced. What they have done is use a common hole for both patterns and hence the back plate is out of balance,. it appears that this is common practice for most of the smaller lathes with bolt on chucks.

When you mount a chuck the bolts effectively replace the metal lost to drilling the back plate, however this leaves the remaining holes which unbalance the back plate. If 3 stud chuck is fitted then there is 1 hole diametrically opposite one of the bolts that causes imbalance and when a 4 bolt chuck is fitted then there are 2 holes, each at 30 deg, from the common hole that are vacant and cause imbalance.

Cheers

Martin

Edited By Martin W on 05/11/2015 00:34:53

My lathe is similar, but what does it matter ?. How often do you run with an empty chuck? Getting it balanced with a big lump in the 4 jaw is harder.

Mmmmm... There is a lot to think about there. I can see where the problem lies, after the explanations it seems logical. Apart from Michael's solution, which may be the best one, it appears that there is a juicy problem to solve!

As Gordon says, 'what does it mater', overall, if you are above or below those rpm limits then the answer is; not much. But it is not the fact I was running with no load. If it runs like that without a load, what happens if an unbalanced load is placed in the chuck to start? It may just happen that you get the imbalanced load in the right place to get it all to balance, but what are the chances of that? More than likely, it could, potentially, make things worse. And if you are trying to work within set tolerances things might get frustrating!!!

So, my options are; MadMikes suggestion, Martin's suggestion (which, Martin, I have done. And downloaded and printed the articles, thank you.) Joining John in a padded cell with a pack of headache pills. Or, sitting down with a cup of coffee, watching the world go by as it fixes itself!!

Thanks all for the replies, cheers, Colin.

If you really need it balanced, you could drill 12 holes and do it that way, but why bother.

Ian S C

.

Getting dangerously close to chain-drilling

Take a deep cut and the chuck drops off

MichaelG.

[only kidding]

Not sure that what I am going to describe will make sense...

If the flange (fig 33 on the ARC site) is marked on the edge where the face is blank, opposite the two holes, then the chuck is fitted, mark the chuck, drill to a depth in the chuck to the same width as the flange, That should then bring it to balance without drilling more holes in the flange. Whether this is advisable I'm not sure, so any comments would be appreciated!

I know that I may be being a bit finicky, but I do like to have things running right.

By the way, I like the comments by Michael G!!!

Colin.

Update!

I've just had a phonecall from Ketan of ARC. He explained why there could be a vibration on the machine and the steps for curing it.

I will go through the process in the next couple of days and report back as to how it went.

But can I say that it is not very often these days that a company will ring you up to help with a problem off of their own back.

So, well done ARC and Ketan and Ian for providing a service that, for all they knew, could have been one very irate customer with an axe to grind.

Many thanks, Colin.

Well, I've completed the strip-down and rebuild of the lathe. I followed the instructions given by Ketan and the 'Dismantling and Reassembly Guide' on the ARC site. I'm pleased to say that the vibration has now gone.

There were a couple of minor differences between the model of machine used in the article and the one I have now, but nothing that could not be overcome. The only thing I was not able to do, was to adjust the motor about a couple of mil towards the headstock end to stop the belt from chaffing on the cover, and to prevent it rubbing on one side of the splined motor pulley disc. The cover chaffing was remedied by filing a small cut-out in the cover edge. As for the pulley, it is only just catching and I have moved the belt slightly, so I will probably live with it. Unless, of course, I was missing something!

All in all, it was a great way to get to know your machine and I can thoroughly recommend anyone new to lathes or similar machines, to take the time and effort to do the same. So, a big 'Thank you' to all who replied to my plea for help and an extra 'Thank you' to ARC and Ketan for taking the time and trouble to phone me up and give advice. It was really appreciated and I am very impressed!

I do have some more questions. But I will put them in other posts. I think I need to post them in the 'Tools and Tooling' department! Although they are still in the 'newbie' category. So, don't shoot me if they are in the wrong place!!

Many, many thanks to all, Colin.

Martin W: Ah yes, as I said "as long as no two holes are one" - which is exactly what they have done of course. Silly really, when drilling one extra hole it would be fully balanced.