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MDF vs. Hardwood for Box Joint Jig

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Forum topic by bsh78 posted 06-02-2015 01:01 PM 1052 views 0 times favorited 13 replies Add to Favorites Watch
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bsh78

4 posts in 552 days


06-02-2015 01:01 PM

I have a simple shop-made router table, and I want to make a box joint jig for it.

I figured I’d install two parallel miter channels in the router table and then steel miter sliders on the box joint jig.

I am planning to use hardwood for the key, but do I need to make the rest of the jig out of hardwood too?

Is there any reason why MDF wouldn’t do instead?


13 replies so far

View brtech's profile

brtech

893 posts in 2382 days


#1 posted 06-02-2015 01:55 PM

MDF is my go-to choice for jigs. It’s flat, stable and inexpensive. The stable part is important. OTOH, many jigs have smaller parts with lots of machining, for which hardwood is a better choice. So I usually end up with MDF for the flat parts and hardwood for the smaller bits.

I’m not sure having two miter slots is really worth it. It would be more accurate to hold a jig so that it reliably moves the workpiece in a straight line, but lots and lots of parts have been cut on a single miter jig. As long as you have accurate miter slots and no play in the slider, one should be fine. Two is better, but they had better be parallel to one another big time in order to get any value.

View HornedWoodwork's profile

HornedWoodwork

222 posts in 674 days


#2 posted 06-02-2015 01:56 PM

MDF is a perfect jigging material, it’s reliably flat, cheap, and stable. I keep a slab of 1/4, 1/2, and 5/8 around most of the time in order to make jigs and patterns. The only thing I would caution you about is that unlike solid or ply wood MDF has a tendency to create little piles of material at the cut or drilled edges which need to be sanded or filed to make the surface flat again. Outside of that you are going to be ok.

-- Talent, brilliance, and humility are my virtues.

View timbertailor's profile

timbertailor

1591 posts in 884 days


#3 posted 06-02-2015 03:13 PM

I disagree. MDF is hazardous to your health and the fine dust is almost impossible to control.(contains formaldyhide) And here in the south where humidity is an issue, MDF is NOT stable. It warps in high humidity and has very little, if any, strength over its length.

MDF does not take screws or nails well and tends to dimple or bulge when you use them on MDF.

Go with a material that is FAR more stable. Birch Plywood. It holds screws better, far stronger, far more stable, and is not really affected by humidity.

P.S. and try not to mix materials when making jigs. Different expansion rates for different materials is not good for a jig or work fixture like a router fence.

-- Brad, Texas, https://www.youtube.com/user/tonkatoytruck/feed

View johnstoneb's profile (online now)

johnstoneb

2143 posts in 1632 days


#4 posted 06-02-2015 03:19 PM

For jigs It’s hard to beat Baltic Birch plywood. Everything timber tailor says about MDF I agree with 100% plus it chips and breaks easily.

-- Bruce, Boise, ID

View Fred Hargis's profile

Fred Hargis

3926 posts in 1953 days


#5 posted 06-02-2015 03:32 PM

I like MDF for some jigs, but not this one. BB would be my first choice.

-- Our village hasn't lost it's idiot, he was elected to congress.

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AZWoody

693 posts in 683 days


#6 posted 06-02-2015 05:41 PM

Aside from the other bad things about mdf, the corners do not hold well and tend to get beat up and and can round after time from my experience, so using it for a jig to guide a router would make it less than ideal.

I definitely would go for baltic birch ply, or even better, some other solid, stable wood for the actual router guide portion of the jig.

View hhhopks's profile

hhhopks

645 posts in 1837 days


#7 posted 06-02-2015 06:00 PM

MDF is heavy. Weight should be part of the consideration. BB would be better. I spied a pieced of plywood with some kind of vinyl covering on one side at work from a shipping box. I am thinking of saving it from the dumpster as the vinyl side appears to be a very nice sliding surface. It weighs about the same as regular plywood.

-- I'll be a woodworker when I grow up. HHHOPKS

View Richard's profile

Richard

1898 posts in 2150 days


#8 posted 06-02-2015 06:39 PM



I disagree. MDF is hazardous to your health and the fine dust is almost impossible to control.(contains formaldyhide) And here in the south where humidity is an issue, MDF is NOT stable. It warps in high humidity and has very little, if any, strength over its length.

MDF does not take screws or nails well and tends to dimple or bulge when you use them on MDF.

Go with a material that is FAR more stable. Birch Plywood. It holds screws better, far stronger, far more stable, and is not really affected by humidity.

P.S. and try not to mix materials when making jigs. Different expansion rates for different materials is not good for a jig or work fixture like a router fence.

- timbertailor


I would agree with this as well , if there is any chance of getting it wet it will swell up and be unusable unless it is sealed very good to prevent water getting to it. And when cutting it make sure to use a Respirator or at least a good mask of some kind. I would go with Baltic birch plywood or at least a good AC plywood.

View Blackie_'s profile

Blackie_

4530 posts in 1972 days


#9 posted 06-03-2015 10:46 AM

MLCS makes a jig, it’s made from MDF, might give it a look and copy that design, I have and use it, also did a review on it.

http://lumberjocks.com/reviews/3539

-- Randy - If I'm not on LJ's then I'm making Saw Dust. Please feel free to visit my store location at http://www.facebook.com/randy.blackstock.custom.wood.designs

View woodenwarrior's profile

woodenwarrior

203 posts in 1654 days


#10 posted 06-03-2015 10:59 AM

For a jig you need only for a couple of cuts then tossed in the corner, MDF works fine. If it’s something that you would like to use over a long stretch, BB is the way to go. Additionally, I find that jigs I fabricate from MDF loose their accuracy fairly quickly. This is the rule of thumb I use in my shop.

-- Do or do not...there is no try - Master Yoda

View rwe2156's profile

rwe2156

2187 posts in 940 days


#11 posted 06-03-2015 11:03 AM

I don’t use MDF anymore for anything for all the reasons previously posted.

Go with BB ply.

-- Everything is a prototype thats why its one of a kind!!

View bsh78's profile

bsh78

4 posts in 552 days


#12 posted 06-07-2015 06:08 PM

Thanks for all the replies, everybody.

Maybe I will give baltic birch a try. Seems like the main trick is finding out where to buy it.

Anyone else have any thoughts on using two miter slots versus one?

I figured I could use the miter slots on a table saw to get the two sliders lined up parallel on the jig. And then maybe use the sliders on the jig to set up the miter channels parallel in the router table.

View bbasiaga's profile

bbasiaga

754 posts in 1455 days


#13 posted 06-07-2015 06:22 PM

BB is nice, but I have to drive 90min to find some. So I use MDF for a lot. I just roll my TS outside the garage to cut it. I wear a respirator anyway, even with regular wood. The taper jig I have made from MDF with some key components from poplar is holding up well.

With a box joint jig though, I would tend to agree that the parts contacting the router guide are likely to round over . Not sure how fast though.

-Brian

-- Part of engineering is to know when to put your calculator down and pick up your tools.

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