MDF

Re: MDF

john lucas

The only reason to use MDF for the purpose he uses it on page 74 is because it's really stable and should last a long time. For a one time project I would think anything that you can cut a square rabbit in would be fine. Especially since he coats it with Blue tape. I don't see why plywood would not work just as well for that purpose. For that matter a 2x4 that's good and dry and milled properly should work.

Re: MDF

Jeff luedloff

you can get small pieces of mdf at the local menards home depot's etc- i believe they have 2'x2' pieces

Re: MDF

ebd

I don't have the book so I don't know what the jig is.

I made my dedicated (specific angle set to perfection and locked down) sleds, to cut segments, from plexaglass/acrylic sheet. I do a lot of simple segmentation. Worked so well I made a sled for 45° cuts. Perfect every time.

It's way thinner than MDF, doesn't chip, totally impervious to water, oil, solvents, etc. and you can get the size you need from pretty much any glass/window repair shop.

FWIW, MDF warps

GaryG in MD

This may not be important for your application, but I made a 12" "disc chuck" for using as a jam chuck to turn the bottom/foot area of bowls (I don't have vacuum and find a donut chuck kind of dangerous). It's kind of like using Cole jaws, but you can turn a little ridge for the rim (or not) and have to keep the tail center up on a small nub. Anyway, I thought MDF would be a good substitute for plywood. NOT. It warps like crazy. Every time I use it, it gets more like a pretzel. I have to re-true it (by a lot) every time I put it on. I keep it in a cool, dark, fairly constant temp and humidity environment with no stresses on it. It really surprised me that this happens. Does anybody understand why this happens? Comments welcome.

My next one will be plywood! ...GG

Re: FWIW, MDF warps

mikeee12345

Corian material is another great material to use for jigs.

You can cut it on a table saw and it drills easily and you can glue it with CA glue.

Very stable material, you can also use a router or milling bits on the material.

Re: FWIW, MDF warps

John K Jordan

How about sealing it all over after machining?

JKJ

that might help

GaryG in MD

but it would have to be done after each use.

That, of course, is doable.

Can't hurt. I may as well give it a try.

Great thought. Duh. Why didn't I think of that?

good to know

GaryG in MD

Thanks for the info, Mike.

Might be a little heavy should work.

I didn't use plywood because I don't like to turn it.

I know Corian is turnable, but I'm not sure I'd like the residue.

Definitely need the vacuum!

Re: FWIW, MDF warps

john lucas

Plywood does also in that application. I have a disc that's about 16" in diameter that I use every once in a while to jam chuck a piece or to center it. Seems like every time I use it (which is probably about once a year) I have to return it to true it up. Not a lot but it's never flat.

yep

GaryG in MD

Plywood makes sense because of the directional stability obtained from the crossed plies, but I don't like to turn it (voids, glue, those different directions, etc.) Yes, I could buy the expensive stuff...

What I don't understand is WHY is the MDF warping. It's amorphous and has no inherent directionality. I've been careful not to put mechanical stresses on it in storage (or, at least I thought I didn't). I keep it in a place that is very environmentally benign (my wine cellar!). So why is it warping? Makes me crazy.

Re: yep

john lucas

Personally I would rather turn plywood than MDF. MDF just turns to powder and is really nasty. Plywood isn't fun either but turns pretty easily with sharp tools. As for why the MDf is moving I don't know either. It moves easily with weight on it or if moisture gets on it but usually doesn't when just left alone.

Re: FWIW, MDF warps

William Duffield

There are a couple of reasons MDF is unsuitable for this application. It is much denser on the manufactured surfaces than in its core. It is not nearly as stiff as real wood, or even plywood or OSB. I guess this is due to what has been done to the wood fibers in the first stages of manufacturing. There is not a lot of glue in the center. Most of it is on the surfaces. It swells quickly and drastically when it gets wet. It expands and disintegrates when you drill holes or drive screws into it.

What About OSB

Stuart Johnson

I have a bunch of 8" x 4' strips of OSB. Would several of these glued up be any good as a glue block?

Re: What About OSB

john lucas

Not as a glue block. I have had pretty sizeable pieces of osb veneer peel off when working with it. I remember one time glueing a bunch up and turning a hollow vessel with it. It was a royal pain. It might work as a jam chuck which is what we were discussing above but I would not use it as a glue block.

Re: good to know

Robert Lalonde

I bought one of Bob Leonard's Frugal Vacuum chucks a couple of years ago and just love it. It came with a PVC 4" Sewer and Drain coupler for the chuck but I made a new one (actually 3: 2", 3" and 4") from schedule 40 PVC couplers and applied Rubber Chucky bumpers for cushions. This works very well. The bumpers don't wear like closed cell foamies and they leave no marks. Highly recommended.

thanks Robert

GaryG in MD

I use a PVC coupler jam chuck too, on the inside of bowls.

But this application is for holding it by the rim.

Good to know about your bumpers.

agreed about 'nasty'

GaryG in MD

I keep a powerful vacuum cleaner going when I turn it, but it still tends to get "all over". Since I turn outside, it's not as big a problem, but I always wear a dust mask, for sure! And I clearly won't be making anything out of it again in the future! ...GG

I couldn't agree more...

GaryG in MD

I had it left over from making a Mark Gardner multi-axis bowl and thought I'd put it to good use. Well, I put it to use. :-P ...GG

Re: thanks Robert

Robert Lalonde

Hi Gary. This is why I have several sizes of PVC chucks. I can use them on both the inside and outside of bowls and hollow vessels. Bob.