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Forum topic by holzbee posted 03-26-2015 06:51 PM 2034 views 0 times favorited 11 replies Add to Favorites Watch
View holzbee's profile


5 posts in 1155 days

03-26-2015 06:51 PM


Ive been struggling a bit with what seemed like it would be a relatively easy process of making cradled mdf panels to paint on, but being a newbie I ran into many problems and questions. I wanted to outsource it to a proper carpenter but its out of my price range and am now back trying to see if its possible for me to do it right on my own.

Im looking to do something like the 24×24 panel on this page, but I want to make them around 95×78” (7” 11” x 6’ 6”)

1. The first problem is that when I get my straight and 45 cuts from the lumber store, the butt and corners/45s simply do not line up and my attempts to sand them makes it worse. I hear that the cuts from lumber store are not accurate. What equipment, saw and type of blade (tooth/quality), etc. might I be able to get to get proper clean cuts? I dont have a huge budget, but seems most of the cuts I need for the frame should be pretty basic. The MDF I would get cut elsewhere as those come out fine.

2. I need this to be as light but as stable from warping as possible – its for gallery and museum use and needs to be long lasting. What size/kind of wood and how many cross and diagonal braces do I need to calculate at the above size and smaller. I’m planning on using 1/8” mdf, so this is just for the brace.

3. What other tools might I need to make any adjustments if any, such as planers or belt sanders, etc for the length of the wood and the butt ends – things just dont seem to line up for me. I would like the frame and mdf to be flush all around and for the inner joints to be flush as well. Again I dont have much to invest, but I need to get it right. In the end it will be cheaper then outsourcing it.

4. In my limited experience, the fame didnt lay flush with the mdf and I had to use a lot of wood glue to fill in the gaps. Seems this shouldnt be so difficult, but doesnt work. Not sure if its the wood or me or both. :) What’s the best way to do this? I tried making the cradle first and then gluing it and the other way around.

5. I sanded and wiped with a bit of alcohol the mdf, but then it literally drank all my polyurethane I used to seal it. Is this normal? Did I over sand maybe? (as a side question, Im guessing the varnish goes on after the cradle is glued, but its hard to get in all the crevices without pouring it on, but if I varnish all the pieces before, then it doesnt stick good and my attempts to sand the varnish first to give it tooth resulted in my not being confident that all the surfaces were varnished).

Thanks for any advice or links to how to do this right.

11 replies so far

View BinghamtonEd's profile


2298 posts in 2367 days

#1 posted 03-26-2015 07:23 PM

My initial thoughts are what you’ve already mentioned, that you’re lumber probably isn’t straight and the cuts aren’t precise either. That’ll make it near impossible to build a square frame.

You could try sourcing S4S lumber at an actual hardwood dealer. Birch or poplar would work, and I know my local place carries S4S in 1/2” thickness and it’s cheaper than HD or Lowes.

Since there are many miters here, I’d recommend investing in a powered miter saw. If this is all you’re using it for, you don’t need a compound or sliding miter saw. You don’t need the most expensive one nor the one with the most bells and whistles.

If you can get the S4S lumber and it’s actually pretty flat/straight, you can build the outer frame, and then the internal support pieces. Depending on the stock, you may need to tweak some of the angles as you go to get the frame square, meaning they may need to be a degree off to end up forming a 90. I wouldn’t do any math for the inside pieces, I would just lay an oversize piece on the frame and mark the two ends with a pencil and then cut to those angles/lines. Measure as little as possible and rely instead on marking the pieces as they would fit in, then cutting to that.

Don’t know anything about finishing MDF (besides painting).

Edit : It looks like they glued (and possibly nailed/screwed) the pieces on to the backer board. That might simplify construction as miters by themselves are not strong. Anything built with 1/8” is going to be pretty weak in regards to shear forces.

-- - The mightiest oak in the forest is just a little nut that held its ground.

View MT_Stringer's profile


3168 posts in 3229 days

#2 posted 03-26-2015 08:32 PM

Do the four corners have to be mitered?

Will the frames be wrapped?

For your job, a ten inch powered miter saw, as Ed mentioned, would make all your cuts, either at 45 deg, or 90 deg. A stop block can be set up so you make the same length cuts each time.

To assemble the frames, you need a flat work surface. That could be as simple as a pair of saw horses and a solid core door. And clamps to secure the frame and top while the glue sets up, if you use glue. Harbor Freight sells some pretty affordable clamps.

-- Handcrafted by Mike Henderson - Channelview, Texas

View holzbee's profile


5 posts in 1155 days

#3 posted 03-26-2015 09:50 PM

Hello and thank you both for replying. What is S4S lumber exactly. Im in Berlin, Germany and would try to find the equivalent. The frame should look very similar to the photo BinghamptonEd posted in terms of miters and everything else. It wont be wrapped, only difference between mine and the photo will be the use of MDF instead of wood for the flat surface (and the number and method of cross braces).

I was looking at this saw:
and if this is good enough, the more important question is what kind of blade do I need for this kind of wood (I guess pine, poplar, birch – whatever I can find here). would the one that comes with it be good enough? I looked at more fine blades, but got so overwhelmed with prices and choices and reviews. Some say too fine can be as bad as too coarse. Whats a good solid blade (quality/#teeth/etc) for the money that will last me?

Lastly, as you can see in the links I posted in the first post, how do I determine how many straight and diagonal braces I need? there seems to be various ways gluing to mdf and floating it.. check out this guys pics at bottom of post:

just need to be sure it doesnt warp over time with the minimal bracing to do so to keep it light.


View holzbee's profile


5 posts in 1155 days

#4 posted 03-26-2015 10:44 PM

p.s. as to the doing it myself with a mitre saw and good blade. will I be able to get a very clean cut? I mean more than the hardware store. When I got my wood cut there, in that case it was only straight cuts, they were not flush. 45s Im sure need to be more accurate. I was told it was because the cuts at the lumber store arent accurate. would me doing it with a good blade get me better cuts? and if not, what can I do to make them even? My attempts to sand them made it worse. do I need some kind of belt or other sander? If the cut is clean seems i shouldnt need another tool, but whatever I need to do to get th job done. :)

View MT_Stringer's profile


3168 posts in 3229 days

#5 posted 03-26-2015 11:17 PM

S4S means “surfaced 4 sides”. It should have square shoulders on all four sides.

The frame you are going to build will not be seen, so to me, it doesn’t have to be furniture quality. But it is important to have accurate cuts. The miter saw should do that. It will be up to you to measure accurately, line up the boards and make the cut.

What is your plan for assembly?

-- Handcrafted by Mike Henderson - Channelview, Texas

View holzbee's profile


5 posts in 1155 days

#6 posted 03-27-2015 08:25 AM

plan for assembly is mostly glue and screws for support frame and glued to mdf.
any suggestions as to what blade to buy?
or any other helpful tools to get the but ends and 45s flush?


View rwe2156's profile


2925 posts in 1478 days

#7 posted 03-27-2015 10:47 AM

Yes, if the cut is accurate you don’t need any other tools.

I don’t really think you need a power miter saw unless you’re either planning on making alot of them or doing alot of other projects.

Basically, a good quality hand miter saw will work very well.
You can make your own miter box or buy a good quality one.
There will be a whole lot less mess to clean up, too.

A simple block plane will suffice to flush the corners.
If you can, a few clamps long enough to span the width will aid in keeping the wood aligned while you drill and screw them together.

I would suggest using any hardwood, as it will be strong and you can use a smaller dimension lumber like 1×2.

Make sure your corner braces are not too close to the corner to increase stability.
Once the panel is adhered, it will not rack, but it will flex if the wood is either too small or not enough braces.

A few finishing nails will keep the panel from sliding during glue up.
Perhaps a caul and clamps on edges will eliminate gaps.

You may also consider another material beside MDF, such as 1/8” plywood.

As you have found, MDF is quite porous. However, it does respond quite well to painting if that’s an option for you.
Use an oil based primer as the first coat.

Either way, using a sealer as the first coat will help.
One option is an oil based product such as boiled linseed oil or a sanding sealer.

On MDF shop fixtures and jigs, I use BLO mixed 50/50 with turpentine and follow with oil based urethane.
This will give an excellent finish and you can adjust the sheen by using satin, semi or gloss.

BLO has quite an odor and takes a long time to dry.
Another option might be a finishing oil such as Danish oil or Tung oil, but it will take alot of it.
I recommend using a small piece as a test.

Good Luck!!

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

View BinghamtonEd's profile


2298 posts in 2367 days

#8 posted 03-27-2015 12:48 PM

any suggestions as to what blade to buy?

- holzbee

I would suggest a higher tooth-count cross-cut blade. Doesn’t sound like you’re going to be doing much ripping, and this blade should give you clean cuts with minimal tearout/splintering.

I don’t know what you have available to you where you live, but I have one of these and I think it is a great blade for the money.

There are various right-angle clamps, usually the home improvement stores stock at least one variation. They can be useful, but they can get pricey if you want to buy 4 or more so you’re not waiting for glue to dry to do the next corner. Something like this would allow you to clamp up an entire frame at once (2 or 3 clamps per corner). The only caveat is that these aren’t going to pull an out-of-square frame of that size into square, so you need to have accurate cuts.

Regarding your question as to the accuracy of cuts at the store…they’re usually inaccurate because either a.) the tools were not set up accurately to begin with b.) they haven’t been meticulously maintained c.) the employee figures close enough is good enough or d.) all of the above. Having your own saw, you can eliminate these factors. You get a decent saw set up right, keep it that way, and you’ll be far more pleased with the results.

-- - The mightiest oak in the forest is just a little nut that held its ground.

View holzbee's profile


5 posts in 1155 days

#9 posted 03-27-2015 07:04 PM

Thanks for the info.. how do I know if that blade which I can find on Amazon here will fit the saw Im thinking of getting? this one:
(but Im open to any good saw for the money – this had good ratings and not too expensive)

I found this blade thats says it goes with it but not sure the quality as compared to the one you recommended. what do I look for to ensure correct fit?

View MT_Stringer's profile


3168 posts in 3229 days

#10 posted 03-28-2015 12:29 AM

I can’t understand a word in either link. But, you first must figure out what size the saw is. Is it a ten inch or 12 inch (most common).

Then check the specs (which I can’t read) to determine the arbor size.
Buy a blade that will match the diameter of the saw blade and the diameter of the saw’s arbor.

Example: I have this saw,default,pd.html?ref=pla&zmam=31282435&zmas=47&zmac=723&zmap=hitnc12rsh&kpid=hitnc12rsh&gclid=Cj0KEQjw_9OoBRChj9vMo5CHrdUBEiQAJ6YRPUz1uRZkDB6ptptMUnHlgzOz_wyn7Z2ft5qkRjyeG3QaAhcV8P8HAQ

It is a 12 inch miter saw and it has a 1 inch diameter arbor.
If I want to replace the blade, I will buy a 12 inch blade (with the desired tooth count) with a 1 inch hole in it.
Hope this helps.

-- Handcrafted by Mike Henderson - Channelview, Texas

View Mark Kornell's profile

Mark Kornell

1169 posts in 2528 days

#11 posted 03-28-2015 06:44 AM

To answer your question #5:

- MDF generally doesn’t need sanding. The surface is meant to come flat and ready for a finish. I can understand wanting to seal it for further finishing, but no sanding should be needed.

- similarly, no need for an alcohol wipe. I can understand wanting to get sanding dust off, but see “no sanding necessary”, above.

- on the first coat, MDF will drink as much polyurethane as you care to feed it. This can be.highly useful in creating a very tough and durable surface. But once that first coat dries, the MDF will stop absorbing polyurethane like a sponge. If all you need to do is seal the MDF, feed it a little by applying about twice as much as you would to a typical surface and let that first coat dry for 24 hours. Sand lightly, then apply a normal second coat. Sand that very lightly to remove dust nibs and apply a third coat. You will have a nicely sealed.surface at that point.

-- Mark Kornell, Kornell Wood Design

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