LumberJocks

Plywood or MDF?

  • Advertise with us

« back to Wood & Lumber forum

Forum topic by JerryinCreek posted 07-29-2015 11:38 PM 1390 views 0 times favorited 25 replies Add to Favorites Watch
View JerryinCreek's profile

JerryinCreek

154 posts in 1302 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

1938 posts in 1449 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.

View lew's profile

lew

11335 posts in 3216 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 852 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.

View JerryinCreek's profile

JerryinCreek

154 posts in 1302 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

1591 posts in 885 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

View JerryinCreek's profile

JerryinCreek

154 posts in 1302 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

2236 posts in 1350 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

380 posts in 943 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

154 posts in 1302 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

611 posts in 1021 days


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

I used MDF for my sled because It stays flat.

View Don10's profile

Don10

26 posts in 865 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

8523 posts in 3109 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.

View JerryinCreek's profile

JerryinCreek

154 posts in 1302 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."

View JerryinCreek's profile

JerryinCreek

154 posts in 1302 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

2190 posts in 941 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!!

showing 1 through 15 of 25 replies

Have your say...

You must be signed in to reply.

DISCLAIMER: Any posts on LJ are posted by individuals acting in their own right and do not necessarily reflect the views of LJ. LJ will not be held liable for the actions of any user.

Latest Projects | Latest Blog Entries | Latest Forum Topics

HomeRefurbers.com