Compression chuck

[GeekMom]

I'd like to make this chuck about 15" diameter:




The plans say to use 1/2" plywood. Could I use scrap 3/4" MDF/melamine instead? Or would the bolt holes hog out too easily?

Thanks!

[RayintheUK]

Karen,

I'd definitely stick with plywood (good quality - no voids). The chuck relies on being able to tighten the pinch bolts evenly and equally, so the bolt heads need a firm recess and the nuts (or wing nuts) need a good surface to tighten onto.

As you suggest, MDF could well hog out with repeated use and it is quite easy to pull a bolt head into MDF, without using much pressure.

Because of the way ply is made, there is much better resistance to such problems. If I WAS going to use MDF, I'd counterbore for a steel washer both sides.

However, bear in mind how much greater a mass that two discs of 3/4" MDF have, compared with two 1/2" ply discs. Whatever you decide, mind your knuckles once it starts whizzing round!

Ray.

[kwgeorge]

Like ray said there will be a lot of mass spinning and probably somewhat off balance so I would not exceed 800RPM.

[guycox]

I actually made mine from 3/4" plywood figuring that more mass that was absolutlely balanced would offset the possible effect of an off centered bowl.

The 2 sheets of ply were taped together and cut using a circle jig on the bandsaw.


The holes is both seets were drilled (at the same time) with a centering jig and are off by a couple of .001s (max). The holes where counter sunk in the drill press for a consistent depth.

The faceplate was mounted and an index mark created on both the faceplate and on back of the headstock-side sheet. The carriage bolts and washers where inserted and tightened up. Carriage bolt heads towards the tailstock.

Then the disks were trued up on the lathe. Create a permanent witness line across the two disks with a sharpie.

The tail stock was brought up to the center of the assembly and the center of the tailstock side disk removed using the parting tool.

Now here's the test... Flip the tailstock disk and if the holes line up, soften the edges of the cutout with some 150grit. Flip the disk back around.

I'm really pleased with mine.. Even on my shopsmith I can spin it up past 800 rpm without it walking across the floor ( not the nickle test but it feels safe).

Get a dedicated faceplate or swab some CA into the faceplate holes to make them last a little longer ( I opted for a dedicated faceplate).

Even after I got the OneWay Mini-Jumbo jaws, there are times when my ply compression chuck does a better job.

When you chuck up a bowl use a inside caliper to get the disks running parallel. You don't have to crank down bolts really hard.


Guy

[GeekMom]

Wow! Thanks for all the quick help!

OK, plywood it is. I'm cutting 3/4" for the back and 1/2" for the front. Thanks for the reminders to run it slower and to keep my hands out of the way!

Guy, the step-by-step instructions will be most helpful. I hadn't remembered to mark an index line or witness line. Will sure save me some headaches in the future if I do it right the first time

[mudder]

Might want to try a longwhrth chuck.

http://www.fholder.com/Woodturning/lwc-wtm.htm

http://www.fholder.com/Woodturning/lwphoto.htm

http://www.crwoodturner.com/longworth/

google search for chuck

http://www.google.com/search?hl=en&l...ck&btnG=Search

[GeekMom]

Thanks, Mudder. That looks like a great plan. (Router goes on wish list . . .)