Drum Chuck Questions -- Success!

[Andy Hoyt]

I was moosing around with a chunk of cherry today and got to a point where it made sense to hold it with my vacuum system. But because of the shape and diameter of key elements of the piece neither my 3.5" or 5.5" aluminum drum chucks would hold it properly.

So I decided to build one that would. I glued up six pieces of 3/4" birch plywood; mounted it to a faceplate; and turned what appeared to be a perfectly serviceable eight inch plywood drum chuck with some thin packaging stuff as a gasket.

But when I when I went to remount my piece I was only able to pull about 5 hg with it and that was absolutely not enough. I remounted one of the aluminum chucks and immediately got 25 hg; so I know the system is okay.

Could it be that I was sucking air right through the plywood?

Should I have sealed it with something?

Would mdf have been a better material?

Your observations are eagerly anticipated. Thanks, Andy Hoyt

[John Miliunas]

Just MHO, Andy, but it seems to me that 6 pieces of BB ply would allow any significant air to pass. Plus, you gotta' figure the glue, which you yourself applied in between the layers, should act as enough of a seal. I would more probably guess that maybe the material you're using for a seal isn't doing the job. Like I said, but just a guess on my part. Let us know if you do determine where the problem lies. I don't have a vacuum setup for mine, but it's on my list....:) :cool:

[Andy Hoyt]

John - Yup, I glued the snot out of it. And the packaging stuff (the kind that electronics come wrapped in inside their shipping carton) is a closed cell foam and has always worked very well for me in the past. I'm stumped on this.

[John Miliunas]

Hmmmm...Well, that being the case, I wonder if air isn't escaping from underneath your sealing material? In that even, maybe you should seal the face of it, before applying the packing material. It's a pretty large area you're working with and maybe the grain of the wood is allowing air to pass from underneath? Just another WAG on my part....:) :cool:

[Jim Becker]

When you make a drum for vacuum chucking, you need to seal it thoroughly...varnish it, shellac it, epoxy it, whatever. Plywood and/or MDF is porous. Check the area where it mates with the faceplate, too.

[Andy Hoyt]

John - Nope. The foam is applied to the rim of the chuck with contact adhesive. No leaks there.

Jim - That's my guess, and I'll seal it tomorrow. And I'll caulk the faceplate-plywood seam too. Thanks.

[Cecil Arnold]

Andy, to reinterate what Jim said, seal every surface. I use yellow glue, slightly thinned with the vacuum pulling it into the wood.

[Andy Hoyt]

Had some success today.

Removed the old foam gasket and retrued the piece
Coated the bejeebers out of the chuck's exterior with a 50-50 (+/-) mix of yellow glue and water
Put a chunk of plywood over the opening
Used the vac to suck the mixture into the pores of the chuck. As I did so she went from 5 hg up to 19hg over the course of ten minutes or so.
Remounted a new piece foam gasket with contact cement. This worked really well. After lunch I turned a platter for kicks and was able to pull 23hg.

Then I completed this thing - which was the cause of all of this. No finish yet - just wiped down with mineral spirts.

Thanks to all of you for your advice.

[John Miliunas]

Well then, Andy. The result was certainly worth the trouble, IMHO!:) That's just too cool! Dang, I'll bet a guy really has to be very aware of the location of one's extremities at all time when turning a piece like that! Maybe, at some point, you can give us a "how-to" pictorial of that process? Very impressive!:) :cool:

[Jeff Sudmeier]

Andy,

That is a wonderful looking peice!! Glad to see your chuck turned out so you were able to finish it! :)

[Andy Hoyt]

Thanks, gents. Actually, the hardest part of the process was to determine the order of the process itself. I did the small "bowl" first, and then flipped it to do the larger "bowl" (which later became the legs). Once turned and sanded, I used the index ring to lay out three points separated by 120 degrees. I then used one of those cheapo laser level thingies to layout a line/arc from point to point. Then to the bandsaw, and then to a long hand-sanding session.

Many others have turned this form, but this was my first stab at it. I'll be trying another and that time I'll dare to be braver with the thickness where the rim of the smaller bowl meets the larger bowl. Will also strive to make the three contact points much smaller. All in all - a good exercise.

Thanks again for your assistance.

And John - since I did the bandsawing at the end it was no less scary than most other turnings. If I could figure out how to do the bandsawing first, then that indeed would impose a degree or two of pucker factor.