4 jaw chucks

Hello all. Having got rid of the mini lathe that blew it's motor, I went mad and bought a rather large lathe from Italy. Lathe seems great & pretty accurate for the money. My problem is I want to add a 160mm 4 jaw independent chuck but don't think I'm at the skill level to make my own backplate. All the chucks I can find are either front mounting, or have the 130mm recess I need but have 4 mounting bolts & not 3. Is there a specific chuck I need to look for, or is there an easy way to mount the 130mm recess chucks, like drilling 3 new mounting holes & not using the 4? Cheers

Hello Arckivio, some more information would be useful, what make is your new lathe, what type if fitting is the spindle, screw on, DIN taper or ???

John

Arckivio

It would be most unusual to find a four-jaw chuck with three fixing holes

I think this illustration might help identify what you need: **LINK**

http://www.boltontools.net/index.php?route=product/product&product_id=2117

MichaelG.

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Edit: Although that plate does look a little strange 

Edited By Michael Gilligan on 06/06/2019 23:12:11

Ha. I never came across that because I searched UK only on Google. Even just the backing plate would do me. I also never searched specifically for the code number of my lathe. Don't want to use the brand name . Thanksas this forum has advertisers and they are not one of them lol. Thanks

If they had a 6" chuck I'd try & order from them. If I got the 4 jaw with the 130mm recess, would it be possible to mark & drill 3 mounting holes?

Yes the spindle has the register, 130mm. The 3 jaw chuck doesn't have a backplate as it already has the matching recess. No studs, the chuck bolts through holes in the spindle. Like I said, I can find a 4 jaw chuck with the recess but has 4 holes.

You can download the manual from the site Michael linked to. As JohnF said it shows the spindle is for direct fit of a 3-jaw. To mount a 4Jaw you need a backplate with 4 holes to it the 4-jaw and 3 tapped holes to take studs or the bolts for mounting to the flange.

It should be possible to find a part machined backplate, what part of the world are you in?

Thanks for the replies everyone. I was trying to avoid the backplate route but looks like the chuck I want doesn't exist. I have seen backplate blanks so might be easier to start with one of those.

For what it's worth, my lathe has a 160mm 4 jaw chuck which uses a backplate with a three hole fixing onto the mandrel.

Actually, it's worse than that as the mandrel has a set of 6 tapped holes in it onto which is bolted a chuck adaptor plate. This plate has three holes which allow for a three hole fixing 3 jaw to be directly attached to it. The 4 jaw chuck then uses a 4 hole to 3 hole back plate between the chuck and the adaptor plate. Seems to work ok. And, many years ago, I made an aluminium backplate to enable me to use an 80mm 4 jaw chuck.

Peter G. Shaw

I've wondered why bolt-on 3-jaw chucks have 3 bolts and 4-jaw types always have four. I think it's probably done to maintain balance and reduce torsional stress inside the chuck as it rotates. Turning forces are generated inside the chuck by the weight of the chuck body as it spins.  If only 3 fixing points are used the forces may be unbalanced by spinning and also by unequal cutting forces via one of the jaws. I've not attempted to work out how big the forces are, but potentially quite big - trying to stop a freewheeling chuck by hand hurts.

If you try a three bolt fixing system can you report back what happens. Three possibilities:

• Works with no adverse effects (hurrah!)
• Works but finish affected by vibration (Might be acceptable)
• The chuck might burst at high-speed. (Tears before bedtime.)

Dave

Edited By SillyOldDuffer on 09/06/2019 12:00:40

Dave it also has something to do with the difficulty of getting 3 holes spaced between the 4 jaws as most 4-jaw chucks are through fixing so you need room for a counterbored hole that does not come too close the the slots for the jaws. The bigger the chuck fixing PCD the less of a problem.

having work off ctr in the 4-jaw will far outweigh any slight balance issues from 3 or 4 fixings.

Arckivio,

Google d1-3 flange dimensions, they are very similar. My Myford has a BS4224 fitting, 3 mounting studs. It takes D1-3 chucks with the camlock fittings replaced by threaded studs. I bought these years ago from the old Myford in Nottingham.

GordoH

I'll look into that fixing too before I do, or buy anything. Thanks for all the replies everyone. Lots to think about and look into.

Well there you go - I hadn't thought of extra holes weakening the chuck!

I'm not explaining the imbalance very well but picking up on Jason's more practical point about spacing the holes here's a photo of a 4-jaw and its backplate:

Drilling new holes to match may be impossible without damaging the chuck.

Is lack of a pillar drill putting you off making a backplate (assuming one can't be bought)? Using a lathe to drill off-centre holes with a faceplate came up recently. Not as difficult as you think once you know how, especially on a big lathe like yours!

Dave

It's not lack of a pillar drill, it's of experience on a bigger lathe doing bigger things. I've gone from a mini lathe to something quite a bit bigger! Looks like a back plate should be my first big project. I found a seller doing 160mm diameter cast iron by the inch.

And this is how close the four fixings of a 160mm lightweight 4-jaw chuck come to the 3 flange studs on my lathe, had they been counterbored holes like Dave's they would have clashed.