Building a Mr Sawdust table - materials

[Paul Schaefer]

I've finally got my MBF put back together. There's a pronounced bow to the old table, so I'm going to need to build a Mr Sawdust table, and I have some questions about materials

I've never worked with MDF before. When I go to the store, can I expect it to be dead-flat, or do I rely on the weights during the glue-up process to flatten the sheets out? Also, I have a chipboard table that I pulled off my old Craftsman RAS, can I re-use that as one of the layers? (It's not a money issue so much as my desire to re-use things whenever I can).

Finally, there's a slight bend to the bars that the table will be mounted on. What's the best way to straighten those out?

[Matt Day]

Mdf will be flat unless abused by the employees, and that's unlikely. Wear a respirator when cutting and be prepared for fine dust to get all over everything. That being said, the stuff is super handy and I use it quite a bit. Flat, uniform, and stable.

If I were you and spending the time money and energy on a new top, I would not try to reuse the chipboard.

The bars should bend with a little persuasion, but they may flatten out with the top on.

[Bruce Page]

Mdf will be flat unless abused by the employees, and that's unlikely. Wear a respirator when cutting and be prepared for fine dust to get all over everything.

It gets all over EVERYTHING!

[Roy Turbett]

There's an interesting thread on this topic at the Delphi DeWalt RAS forum.

[Paul K. Johnson]

I love MDF because it's flat and smooth. It's very easy to finish and even unfinished it lets things slide fairly easily.

My current workbench is MDF except for pine uprights and stringers and the top which is a 1/2" x 4' x 8' piece of tempered glass. The bench was built to build RC planes, not for wood working. The side walls haven't sagged or bowed at all.

I do plan to build a proper woodworking bench eventually.

MDF is great for backer boards when drilling, false/sacrificial tables, filler, etc.

If it gets wet it swells. If an edge gets wet it swells even more. If you plan to make something permanent from MDF and there's any chance of it getting wet then it's best to seal it. Two coats of poly does a great job.

[Earl McLain]

Using Wally Kunkel's book and photos from the site that Roy referenced, I did mine with MDF, topped with a sheet of luan. The only deviation was that I used aluminum instead of steel, but a year later it's still dead flat. Had to recreate the table mounting system on my GWI which would now pull any minor inconsistencies into flat. Great saw.
earl

[Peter Aeschliman]

I would modify this a bit. I would expect a consistent thickness, but don't expect the MDF from HD to be "flat." MDF, even 3/4", is somewhat pliable. If it was stacked somewhat poorly (let's be honest, it usually is), it might have a bow or twist to it. I don't think I've ever bought a piece of MDF that was flat, but it's easy to bend back to flat during glue-up. With the steel bar epoxied in, and a good flat glue-up surface like your table saw table, you'll be able to make it flat.

MDF also is great because it won't expand and contract much. So if you get it glued up flat, it will stay flat.

There are downsides though:

1) MDF is really heavy. So I recommend having Home Depot cut the sheet down for you. It's a PITA to move around otherwise.

2) The dust is horrendous. Wear a mask. If you can, do most of your cutting outside. The super fine dust will coat your entire shop, and it has nasty stuff in it. So you really don't want to breath it in.

3) Don't get it wet

4) as I mentioned, MDF for table tops needs to be well supported in order to be flat. Otherwise it will sag.

Please post pics of your project! I have two MBFs that I'm going to put right next to each other, and they'll share a common super-sized Mr. Sawdust table. I could use some inspiration!

[Peter Aeschliman]

Oh, and to answer your question about flattening the steel bar stock. Which way is it not straight? Is it crooked or bowed? If crooked, I would get a roll of adhesive-backed sand paper and stick it down to my table saw top. Sand it down to get one side straight, then use calipers to mark the parallel side. Then I'd just carefully sand the other side in the same manner, finessing it to make it parallel to the other side.

If bowed, then I'd just force it into the slots you cut in the MDF- it will conform easily.

[Charlie Velasquez]

Paul, as mentioned earlier, don’t skimp on your table. Everything is referenced from your table, not just your stock, but also your initial set-up adjustments and future tuning. The MBF is a nice saw, capable of pretty good accuracy as long as it is set up right.


I am assuming the table rails are the common stock steel like these
.mbf.JPG

Dewalt quit making that style and went with angle cleats like these.
Table-Mounting-Brackets-w-Clamps-Hardware.jpg DW7770.JPG

As you noticed the flat stock rails are prone to deformation. The angle cleats are much more rigid and easier to adjust.


Buy some angle and drill a couple of holes on the sides of the base. If you make a Mr. Sawdust table the steel will keep it rigid length-wise. Makes life a lot easier adjusting.

[Phillip Gregory]

I used generic Unistrut to make the table support for my DeWalt GE. I put two nuts and two washers between the base flanges and the bottom of the strut to work as stop nuts to adjust out any sag or bow. I made the two pieces of laminated MDF with steel spines and topped it with Masonite as recommended by the Delphi forums. This works well on a saw with four struts such as a GA or GE that is stored indoors, but I'd go for two pieces of 11 or 13 ply 3/4" laminated plywood as Wally Kunkel recommended with a GW or MB series saw with only two supports on the sides and a big saggy unsupported span in the middle.

You will make your grooves for the steel bars deeper than the steel bars so that any irregularities in profile of the bars gets absorbed by the depth of the slots. I made mine 1/16" deeper on each piece than the steel bars. This also provides a place for the extra epoxy to squeeze into. The weights will push everything flat during glue-up.

Get rid of the chipboard, it is garbage.

[Paul Schaefer]

Here's the MDF table and lauan sacrificial top with shellac and three coats poly:
20170626_210959.jpg

Angled cleats and side-mounting to the table is like the system on my old craftsman RAS, and I HATED it. Tightening the bolts between cleat and base would move the cleat, so adjusting the saw was awful. I'm going to go with running the bolts through the top, though Charlie makes me think the original bar stock might not be rigid enough. Anyone re-used the original hardware and been happy with it?