Sieg C3 Chuck run out

Sieg C3 Chuck run out

I have always had a slight run out problem with my lathe and would like to change the chuck, I’m by no means an expert and would appreciate some advice here are the readings I’m getting from the standard chuck in MM

Spindle run out .04

Spindle face .01

Chuck run out was .06 which I got down to .01

To me all seams well but when I place some bar in the jaws things go everywhere

Bar in jaws depending on the bar I have had .10 at best and .13 worst now if I rotate the bar I can get this down to .08 to me this seems as the jaws could do with a grinding but I don’t have the kit to do this, is there a replacement chuck 80 to 100mm that is more suitable

Edited By Chris Trice on 21/05/2014 00:33:43

Over on another forum, one of the chaps there found that lots of chucks have a mark by one of the key holes. He found that if you use this key slot to tighten the chuck it is more accurate than using any of the other key slots. I have not checked this out myself as I had forgotten about it until reading this thread. I must give it a try sometime.

Cheers Derek.

Isn't this why the four-jaw independent chuck is preferred for accurate work?

Cheers, Tim

Hi.

If you are able to change the measured run out by rotating the bar in the chuck then I would check the bar, especially if you are tightening the chuck in a similar manner each time. Depending on use/abuse the chuck could be suffering from bell mouth in which case it may need replacing or at least a new set of jaws. As Tim says if you want accuracy then use a 4 jaw chuck and clock work piece until it is running true. If you only want to use a 3 jaw chuck then mark the work piece to a particular chuck feature and realign marks when returning work to the chuck, this at least gives you some chance of reducing the effects of any run out. Normally on standard lathes all turning operations are completed before the work piece is removed to combat run out problems.

If you want to minimise run out then using a collet chuck would help. Something like one of the ER series on a taper to match the spindle of the lathe. ER25 sets run from about 0.5mm through to 16mm.

Cheers

PS

Chester quote, catalogue extract,  that their chucks are:-

"All chucks are fully ground and work to a permissible error of 0.064mm at 50mm from chuck jaws. Each chuck comes with 1 set internal and 1 set external jaws and chuck key."

Martin

Edited By Martin W on 21/05/2014 10:01:28

Martin, I have noticed this problem for a while and have used various bars all have the same results, twist the bar in the chuck and eventually you find an area that’s not as bad, personally I put it down to the chuck after all a C3 is by no means top of the range I would hazard a guess that replacing the chuck with almost anything would give better results I thought someone would have had similar problems and be able to suggest a chuck

If you want accuracy on a hobby machine then you must support your work from the tailstock end

To think otherwise is dreaming

My hugely stiff Drummond is only ever really accurate if I use the tailstock

And If I look though 50 years of the "Model Engineer" from 1940 to 1990 do I find a single poster complaining about "chuck run out" ????

I did get a hit from the "Excel Small Tools Catalogue"

Edited By Ady1 on 22/05/2014 01:01:50

I would think that if you have .04mm spindle runout you will struggle to get a new chuck to run any truer than that.

Even my 75 year old Drummond with bronze bearings in the headstock clocks zero runout (less than the width of one of the lines on the dial.)

It may be that your headstock bearings need attention/adjustment.

Yes, most older/quality chucks will have a mark on the key hole that was used when the jaws were trued at the factory and if you use this hole you will get more consistent results.

Grinding the chuck you have is easily done with a dremel or electric drill held in the toolpost and a "cloverleaf" plate made out of scrap with four holes drilled/bored in it to push the jaws outward while grinding the inner faces. Worked a treat on my bellmouthed old Crown chuck on the mighty Drummond.

I'd post a pic of my set up but bloody Photobucket is down for the count at the moment.

Hi Hopper

I'd be interested to see a pic of this "cloverleaf" plate if you're able to once PB is back up.

Cheers

I am not sure exactly how your chuck assembles onto it's backplate. But on my myford std 3 jaw chuck, I put some bellvill washers under the capscrews. Then it allowed me to lossen the retaining screws a little, and adjust the workpiece to zero , then I tighten them up. Older chucks tend to have areas where they run well and areas where they are not so good. Since it was not right, I made it adjustable. On my chuck backplate I trimmed the spigot diameter down a bit to allow for the adjustment.I also trimmed an allen key down to get in behind easily.

Neil, If you can not make it right, make it adjustable.

Ady 1 is more than correct about seeing much or any mention about chuck runout in those old M.E. magazines. But I'm way too lazy to retype it all again. If your interested enough, then please have a read through of what I just posted in the "Square Top Colch / Student" thread in this same sub forum. Since both threads are a bit alike I couldn't make up my mind where to post the information.

Pete

This topic continues to come up. I've just nipped in the shed, fitted my self centering 5 inch TOS chuck (which are in the £200-£300 range now and the backplate was machined in situ on my Sieg C6B). I made sure all the mating surfaces between back plate and spindle were scrupulously clean. The spindle has a centre pop mark to align to a centre pop mark on the backplate, so it goes on in the same place it was machined everytime.

With a piece of decent bar in the chuck, tightened on the square marked with a "0" and then nipped up on the other, the runout is +/- 0.02mm (0.04mm TIR) 25mm from the chuck I am chuffed to bits with that.

I'll measure the runout on the chinese chuck that came with the lathe if I get time, but it really isn't worth bothering about.

Repeating what's been said above, use an independent jaw chuck and clock the workpiece if better accuracy is needed. Or don't remove the workpiece until all the concentric features have been completed.

I'm not an expert, but grinding jaws is an action of last resort to recover what is other wise a scrap chuck isn't it? Doesn't it mean the runout is only good at the position they were ground?

Must go back in the shed to make some more bits for that steam engine...

Steve

The run out on a three jaw SC chuck will most likely be different depending on the diameter of the work being held in the chuck, if you use a great amount of material that is the same size, you may have greater wear in that part of the scroll. Ian S C

This is one option, three of these in between the jaws sized to suit the chuck

Edited By Bob Brown 1 on 08/06/2014 13:40:15

clover plate , not my picture, from a google search.

Right chaps, after a bit of time checking as much as possible I have a few conclusions firstly some of the bar I was using is not quite round I know this as I have had some blanks machined by an engineer who I know will and has a very accurate machine having worked in the arms industry, even he said not to trust off the shelf bar, so with a machined blank in hand I tested the chuck run out again what I found was tightening one key proved to be more accurate than the other two but still I had a lot of run out more than would be acceptable, after trying all I know I was at the point of buying a new chuck so thought “what the hell” and decided to grind the jaws with a Proxxon and home-made mounting kit, what I found was only one jaw was hitting the grinding wheel after a very light pass, so again I tried grinding until all three jaws had been ground then I tried my trusty insert and what would you know the chuck is now running almost perfect so the problem was always a cheap Chinese chuck, I repeated this with the outer set of jaws these were even worse

How many times have I read such threads? Anyway are you in fact measuring what you perceive to be runout? By this I mean clocking a piece of piece of pre-machined round bar after you have fitted it into the chuck. If so you are frankly worrying about the wrong things in life.

Take a piece of round bright steel bar and machine it without using a steady or a centre for about 50 to 75mm of its length. Then measure the runout, if there is any, on the bar that you have machined without disturbing the chuck jaws in any way. You will then see if you have real, rather than perceived, runout.

What matters is not what you see on the chuck but what is produced when you turn the bar. Remember that 3 jaw self-centring chucks are not accurate when measured in isolation from the cutting process, are often inconsistent when clamping, and are simply holding devices. What you produce is the important thing when turning. HTH.

I'd be interested in the runout you are measuring at different diameters and what you consider to be "almost perfect"? Grinding chuck jaws I've always considered to be a recovery job on worn out old jaws, I can't see how it improves the accuracy of the chuck itself.

Steve