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Plywood or MDF?

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Forum topic by JerryinCreek posted 07-29-2015 11:38 PM 1492 views 0 times favorited 25 replies Add to Favorites Watch
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JerryinCreek

187 posts in 1507 days


07-29-2015 11:38 PM

Topic tags/keywords: jig

Making a new sled for my tablesaw, 18×32. What is more stable for the base, 1/2” ply or MDF?

-- Jerry, Johnson Creek, WI "If it was meant to be different it would be."


25 replies so far

View Redoak49's profile

Redoak49

2506 posts in 1654 days


#1 posted 07-29-2015 11:45 PM

I prefer Baltic Birch plywood for jigs that I will use a lot. For a one time jig, cheaper plywood or mdf is ok. I just do not like the dust from cutting mdf or the issues with putting a screw into it.

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lew

11612 posts in 3421 days


#2 posted 07-29-2015 11:57 PM

Also, slots that capture carriage bolt heads tend to chew out faster with MDF

-- Lew- Time traveler. Purveyor of the Universe's finest custom rolling pins.

View JeffP's profile

JeffP

573 posts in 1057 days


#3 posted 07-30-2015 12:21 AM

For a sled, warping is the worst. I’m sure MDF can warp, but I have seen a lot more pieces of bent plywood than mdf.

It could be that more expensive types of plywood are more stable against warping/twisting/bending than cheap mdf and/or cheap plywood. Don’t know.

I would suggest you start with MDF and think of it as a “prototype” sled. Then after you have some time with it and some new ideas about how it should be designed…then build one with expensive grade of plywood.

The slot runner should definitely be made out of UHMW (Ultra High Molecular Weight Polyethylene)—or HDPE (similar but cheaper stuff) the stuff that walmart cutting boards are made of. The slot runner has to be extremely close tolerance with the slot and very stable over time/temp/humidity in order for the sled to work well. Either an extremely stable hardwood, or UHMW/HDPE. Otherwise the sled will be sloppy in the slot some of the time and bind up other times depending on the weather.

-- Last week I finally got my $*i# together. Unfortunately, it was in my shop, so I will probably never find it again.

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JerryinCreek

187 posts in 1507 days


#4 posted 07-30-2015 12:37 AM

The runner is a non-issue as I have an Incra to use from a prior project.

-- Jerry, Johnson Creek, WI "If it was meant to be different it would be."

View timbertailor's profile

timbertailor

1592 posts in 1090 days


#5 posted 07-30-2015 12:37 AM

MDF has NO redeeming qualities and is terribly hazardous to your health. MDF does not like moisture\humidity and has no strength. It is only as flat as what supports it. Plywood is far stronger and more stable.

Use the best quality Baltic Birch Plywood you can find BB\B. It has been the cabinet makers standard for good reason.

True Baltic Birch comes in 5’x5’ sheets.

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

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JerryinCreek

187 posts in 1507 days


#6 posted 07-30-2015 12:42 AM

Ok, I’ve heard some good arguments. I’ll go with BAltic Birch Ply. I was going to use 1/2” material on this 18×38” sled, any good reason to go with 3/4” (except to build my biceps)?

-- Jerry, Johnson Creek, WI "If it was meant to be different it would be."

View lateralus819's profile

lateralus819

2240 posts in 1555 days


#7 posted 07-30-2015 12:54 AM

A good BB ply is so much nicer. I love the look of BB.

View skatefriday's profile

skatefriday

387 posts in 1148 days


#8 posted 07-30-2015 12:59 AM

BB typically comes in metric units, but I don’t see any need
to go thicker than the 12mm stuff for a sled. Your runners
and fences are going to provide stability anyway.

View JerryinCreek's profile

JerryinCreek

187 posts in 1507 days


#9 posted 07-30-2015 01:01 AM

Excellent! Thanks all!,

-- Jerry, Johnson Creek, WI "If it was meant to be different it would be."

View WhyMe's profile

WhyMe

806 posts in 1227 days


#10 posted 07-30-2015 01:29 AM

I used MDF for my sled because It stays flat.

View Don10's profile

Don10

32 posts in 1070 days


#11 posted 07-30-2015 02:07 AM

Hi Jerry,

I need to make a sled for my new saw too. Are you using any special plans? Looks like BB ply has won out. I vote for UHMW for the runners embedded into a dado slot. No screws needed – just a press fit and a little cryogenic adhesive.

-- Don, Silver City New Mexico, parsimony, utility and elegance - blueprint for any project.

View PurpLev's profile

PurpLev

8525 posts in 3314 days


#12 posted 07-30-2015 02:13 AM

for sleds I like phenolic-faced plywood. has the stability of plywood, with the slickness of phenolic – best of both worlds.

-- ㊍ When in doubt - There is no doubt - Go the safer route.

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JerryinCreek

187 posts in 1507 days


#13 posted 07-30-2015 02:51 AM

Don, I’m replacing the big Bertha Beast I made (accurate but a beast to handle). I’m also replacing the Woodsmith Shop one I made (available on-line WoodsmithShop, 2010). I liked the basic design but the fence is too low and you need an auxiliary fence for any cut longer than 20”. So, I’m using the basic plan but expanding the length and not using the Kreg Top Trak with Stop. Instead, I’ll use a T track and a sliding stop.

-- Jerry, Johnson Creek, WI "If it was meant to be different it would be."

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JerryinCreek

187 posts in 1507 days


#14 posted 07-30-2015 02:53 AM

PurpLev, love that idea! I’ve used contact cement with Formica before, this sounds like a much better idea – thanks!

-- Jerry, Johnson Creek, WI "If it was meant to be different it would be."

View rwe2156's profile

rwe2156

2542 posts in 1146 days


#15 posted 07-30-2015 09:57 AM

No question MDF less likely to warp, but a good grade ply will work.
Remember the front and back fence keep things straight.

Make sure you wear your respirator when cut MDF!!

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

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