Drum Chuck Questions

[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

 

[bbrussell]

I would have used MDF, Although I have never used plywood for this purpose I Would not hesitate to use baltic birch for this purpose and I would seal it with yellow glue. I also would take a look at the packaging material. If you can blw through it, it will not seal.

 

[Andy Hoyt]

Thanks. I'll be sealing it today and give it another go.

The packaging material is a closed cell foam and I've always had good luck with it.

 

[hockenbery]

I make a lots of vacuum chucks by face glueing constuction lumber mounting it on a faceplate and turning a custom fit.

My secret sealer is DUCT tape. It seals instantly and comes in designer colors.

I also seal the faceplate attachment with a bead of hot-melt glue inside the screw holes and a bead of hot melt outside the holes. once the fafeplate is screwed on i run anohtoewr bead of hot-melt around the outside edge of the faceplate where it meets the wood. I then turn the chuck to size and attach the foam with hot-melt.

The nice thing about using these "throw away" vacuum chucks is that you can turn them to fit just about everything and return them until they no longer serve a purpose and make a new one in minutes.

You need to have an good seal against you work piece too. if the work piece is just a bit out of round a second layer of dense form attached with hot melt will seal to a more uneven surface than one layer. however thicker foam makes the mounting a bit spongy and you will have to take very lighter cuts.

happy turning,
Al

 

[Andy Hoyt]

Thanks guys. I sealed the chuck with a 50 - 50 mix of yellow glue and water and this did the trick. Was able to complete the piece that started this mess and get on with things

 

[underdog]

I see you figured it out.

Just as a side note, the shop I work in uses 3/4 MDF as a sacrificial spoilboard on our CNC router table. The vacuum pump pulls a vacuum through it to hold down any sheet goods we're cutting with the Router.

So yes, sheet goods are porous... about the only thing that aren't, are sheets of MDF with melamine (laminate) on one or both sides.

 

[John Trant]

8" diameter with 5 psi is 250 lb of pressure

I'm glad you got it to work but I did want to make one notation. The 8" chuck is quite large and 25 psi from your pump is likely to have applied too much pressure to the turning. This size chuck at 25 psi results in 1,256 pounds of pressure applied to the vessel. The 5 psi (and the resultant 250 pounds of pressure) may have been enough to hold for light cuts.

John

 

[Andy Hoyt]

I'm glad you got it to work but I did want to make one notation. The 8" chuck is quite large and 25 psi from your pump is likely to have applied too much pressure to the turning. This size chuck at 25 psi results in 1,256 pounds of pressure applied to the vessel. The 5 psi (and the resultant 250 pounds of pressure) may have been enough to hold for light cuts.

John

Thanks John. Nope the 5hg (not psi) as read on the gauge wouldn't hold a feather - light cuts or otherwise. Ultimately, I was able to pull about 19hg and this held the piece for heavy cutting. I then reduced it to about 15 for the lighter cuts.

 

[John Trant]

Oops, missed the units!

You are right. I overlooked the units (a mortal sin in my business).

John

 

[Andy Hoyt]

Hey! If that's all you get wrong don't complain. I've screwed the pooch far worse any number of times.