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Discussion Starter #1
So a search for "MDF" turned up nothing here. I'm wondering, what are it's appropriate uses? Specifically, I want to build a manual X Y Z router table. So, I was going to use MDF because it's dimensionally stable, and consistently flat. But, I've never been a fan of "sawdust pressed together" sheet goods, ya know? So, if this IS an appropriate use, how would you fasten it? I plan to make the table slide one way, and a gantry with a carriage sliding the other way, with the Z axis on it. All hand cranked. So it will have to be somewhat ridged, and be able to put up with that hand cranking.
 

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Sounds like a good place to use Baltic birch plywood. I would not use mdf for this application. It is good in compression for providing a flat stable surface, as long as it is in a dry environment (you get it wet and it will swell and never return.) It will also expand and contract some with changes in humidity. I'm sure there are other materials that would work well too. But mdf is not one of them.
 

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Actually my experience with MDF has been that it hardly expands and contracts at all, if any. I used it to make a large panel over 5 feet across and more than 2 feet wide. I mounted this in the headboard of a bed I built and it fits tongue in groove on the top and bottom. On the side posts, it's just butt jointed. It's never separated at all. If it did, I'd see daylight coming through on the sides. I originally chose this because I first made the panel out of pieces of wood fitted together tongue in groove also. They all shrank and I lost 3/8 inch across the whole width. MDF solved this problem completely.

I hope it's not a completely terrible choice for a router table because I'm planning to make one using this also. Not only that but I tore down my jobsite table saw and took the guts out planning to make a new cabinet and large table surface from MDF also. Including the fences for both tables, all MDF. I see it as a cheap material to make a slick surface that is strong, and dimensionally stable to work with, all on a budget.
 

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TooPicky said:
So a search for "MDF" turned up nothing here. I'm wondering, what are it's appropriate uses? Specifically, I want to build a manual X Y Z router table. So, I was going to use MDF because it's dimensionally stable, and consistently flat. But, I've never been a fan of "sawdust pressed together" sheet goods, ya know? So, if this IS an appropriate use, how would you fasten it? I plan to make the table slide one way, and a gantry with a carriage sliding the other way, with the Z axis on it. All hand cranked. So it will have to be somewhat ridged, and be able to put up with that hand cranking.
Before you invest a bunch of time and effort, take a look at the Woodrat, and RouterBoss. No need to reinvent the wheel. Also look at using 80/20 aluminum extrusions. Quite a few of the commercial CNC router set ups utilize the 80/20 extrusions, and they can be bought of eBay relatively inexpensively.

Back to your question: MDF is dimensionally stable. However it is not very good at holding screws from any direction. I would tend towards MDO, HDO, or phenolic sheet, listed in order of expense, and suitability.

The phenolic is the most suitable, but the most expensive. You can sometimes get decent deals on eBay. Another possible source is to talk to local plastics supply houses, and see if they are selling quantities to anyone, and then checking those folks for scraps. It can be drooled and tapped similar to aluminum.

The HDO is second best, but typically hardest to find. Your most likely source is concrete supply companies, where it is sold as forming plywood.

MDO can be bought at most well stocked lumber yards.

All three can readily be worked with carbide woodworking tools.

If you look at the commercial CNC router tables you'll see that the only place they use MDF, is on the sacrificial surface of the tables. Because it is really cheap.
 

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Just to clarify on the expansion and contraction of mdf comment. It isn't as bad as wood, but it does happen. One of the reasons I know this is because I have an mdf router table top. There is enough humidity fluctuation in my shop that I have had to make small tweaks to the height of my router plate in the router table to keep sharp edges from getting caught going onto or off of the plate. I also had a piece that was warped and I could flip the warp from side to side by laying one side on concrete.

For a router table top, it should work fine, as long as you don't cover the top and leave the bottom exposed. Then, it will most likely warp. I would not recommend it for cabinet body or any structural application that will put bending or tension stresses on it. It will break apart fairly easily in those conditions, which is why it doesn't hold screws well.
 

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Discussion Starter #7
The routerboss and Woodrat isn't what I need. Basically, I want a gantry type CNC router, but without CNC capability. And hand cranked, not motor driven. (Although, that would be a nice future upgrade, depending on the cost and parts availability. Not sure what motors to use.) I agree with the comments about MDF. Suspicions confirmed; good as a sacrificial table, terrible structural strength. So not good for much, then.

J-n-F, what is MDO? And, I was somewhat familiar with 80/20, but thought it'd be way too expensive. Turns out it's not really. That looks like a very good option.
 

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Discussion Starter #9
This sounds like a good use for 80/20 and linear bearings. How large do you want the table?
Yes, it does. I'd like to be able to mill anywhere in an 18 x 18" square. And although very cool, linear bearings are way too much money. This project has to be done on a very limited budget. Like less than $200.
 

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Is there a certain type screw that's recommended for MDF? I've worked with it a fair amount and always just used coarse thread drywall screws. I've had one strip out that I can recall. It was when I was driving it with a cordless drill. I've mostly made jigs and subwoofer boxes with it and used glue as well as screws and I haven't had any screws come loose during use. It seems to hold together very well with glue and brad nails. One thing I've made with it was a router caddy, to set a router on while the bit is still spinning but after you've turned it off. I've used this thing a lot, taken it out on jobs, tossed it around, and it still looks just like it did when I built it. Come to think of it, I did notice some splitting occurring as the nails penetrated. The glue has held it solid though.
 

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Is there a certain type screw that's recommended for MDF? I've worked with it a fair amount and always just used coarse thread drywall screws. I've had one strip out that I can recall. It was when I was driving it with a cordless drill. I've mostly made jigs and subwoofer boxes with it and used glue as well as screws and I haven't had any screws come loose during use. It seems to hold together very well with glue and brad nails. One thing I've made with it was a router caddy, to set a router on while the bit is still spinning but after you've turned it off. I've used this thing a lot, taken it out on jobs, tossed it around, and it still looks just like it did when I built it. Come to think of it, I did notice some splitting occurring as the nails penetrated. The glue has held it solid though.
Hi Duane - MDF takes screws and brads pretty well going through the face, it likes to split out going into the edges. Coarse thread drywall hold pretty well but I do recommend pilot holes in the edges if you go that route. Actually, with MDF, pilot holes are a must no matter where you put them. Screws like to split the edges and erupt around the screw when going into the face without the pilot. Personally, I don't use anything but glue on the stuff. I don't feel that additional fasteners beyond glue really bring anything to the party except maybe some grief. If I have a joint that is difficult to clamp, the largest fastener I use is a 23 gauge headless pin. :smile:
 
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