Best methods for finishing MDF

[rogoll]

Re: Best methods for finishing MDF

I had a real mind blowing idea after reading through this thread. :D

What about rubbing on the wood glue (possibly diluted), then lay thin fiberglass cloth over the joints and add a little more glue on top of the fiberglass?

I would imagine it could be made very smooth if you pulled a squeegy over the area.

I need to order some fiberglass cloth and give it a try.

What do you guys think?

I was just looking at the Elmers brand fiberglass products at Lowes. They have fiberglass cloth and fiberglass matte along with the resin and hardener. I'm thinkning of getting some myself just to experiment with.

[Erich H]

Re: Best methods for finishing MDF

I had a real mind blowing idea after reading through this thread. :D

What about rubbing on the wood glue (possibly diluted), then lay thin fiberglass cloth over the joints and add a little more glue on top of the fiberglass?

I would imagine it could be made very smooth if you pulled a squeegy over the area.

I need to order some fiberglass cloth and give it a try.

What do you guys think?

[davepellegrene]

Re: Best methods for finishing MDF

BTW, how did you do the trenches?

Found this. Not to expensive and would allow you to do any depth you like.

http://www.amazon.com/MLCS-Horizontal-Crown-Molding-Router/dp/B000PHA29W

[davepellegrene]

Re: Best methods for finishing MDF

Just got back from my local auto paint store were I bent the ear of the owner for a while. This is what he recommended for what he thought would be the best product he has to fill the trench. Says guys are skimming flexible bumpers with it and not having any flex issues. Says a 1/16th deep groove would be perfect for this stuff.
Dave
http://cgi.ebay.com/ebaymotors/USC-I...motiveQ5fTools

[davepellegrene]

Re: Best methods for finishing MDF

In doing furniture, once you can repeatably produce a square box (ie using a 45 degree lock mitre bit) I generally just use matching standard 45 degree miters w/ clamps and glue for the two remaining panels

But you are a furniture builder. To get all four sides to line up on the top and bottom after you glue the four sides together is not that easy to do.

[CokewithLime]

Re: Best methods for finishing MDF

It does work well if you get the joint set up right. It also gives you a nice square box.
One other issue is you can only do the four sides then you have the top and bottom that will still have a **** joint.

In doing furniture, once you can repeatably produce a square box (ie using a 45 degree lock mitre bit) I generally just use matching standard 45 degree miters w/ clamps and glue for the two remaining panels

[davepellegrene]

Re: Best methods for finishing MDF

"That and I am sensitized to epoxy, so if I don't were full protection I get what is like poison ivy mixed with sun burn with lots of swelling. The only way to get ride of it taking steroid dose packets. Not fun, so I try to stay away from it as much as possible. Anyone can become sensitized to epoxy at any time, so becarefull. One you are sensitized its for life.
Dave

"

Yikes, thats a full blown hypersensitivity reaction, potentially lethal. I'd stay away from anything that could set it off, including testing it for this forum!! Your airway could go into bronchospasm, and your goose, as they say, would be cooked unless you happen to have ready access to an epi-pen.

Seems I am on a roll with tile, marble and Porcelain bathroom jobs lately and you can not beat Epoxy Grout. This is how a became sensitized to it. Took me a while to figure out what was causing it. Most of the time I have my son do it for me. I did have a bathroom last year that I couldn't find anyone to grout for me so I rigged up a suit. I took a tyvec chemical suit with a hood on it and glued a rubber roof vent onto the back of it. Stuck a 3" x 50' flex line on that. I hooked the other end to a bath vent fan and stuck it outside. That blew fresh air into the suit. I then wore a full face shield charcoal respirator, a layer of butyl rubber gloves, a layer of latex gloves then a layer of plastic gloves that went up to my shoulders. It worked but what a pain.
With the little stuff that I am doing with the MDF as long as I wear rubber gloves and keep the air moving, then get out of the room til it dries I am ok.
You are right I need to stay away from it altogether.

[donparsons]

Re: Best methods for finishing MDF

Jim Holtz puts a layer of 1/8" MDF over the whole side panel which would be just about the same thing as a deep rabbit joint. The rabbit would be simpler if you don't break it.This would put the seam on the round over and probably would make it a little more difficult to see.

I definitely think if you can get away from this joint all together would be the best method. Problem is most builders drawings are designed with this type of joint. If one of the methods work it would be possible for someone to redo an existing finish if they don't like the seam showing.

A simple shallow v groove on the seam would do it also and wouldn't look bad.

As far as the trenching goes I just did it on my table belt sander. Would be nice to find a router bit to do it with. I just haven't looked into that yet.
Dave

I did a v groove on the sir audinums I built for my father. It was right between the quilted maple veneer and the solid maple baffle. It looked good.

[davepellegrene]

Re: Best methods for finishing MDF

Has anyone tried using a 45 degree lock mitre bit


I have use these for years with great success in furniture construction - even works very well with most plywoods

I used that joint on my dock box project. I built two boxes then hooked them together. If you look at the top right corner in the pic you can see the joint. I used redwood with epoxy for gluing. I have used this bit a lot building columns in houses. The only problem with using it on MDF is the little tongue on the one piece is cross grain and can break off real easy. If you dry fit the joint you can't get it back apart with out breaking it off. It does work well if you get the joint set up right. It also gives you a nice square box.
One other issue is you can only do the four sides then you have the top and bottom that will still have a **** joint.
Dave

[davepellegrene]

Re: Best methods for finishing MDF

You are probably right Dave, but I wonder if we can do something different in our construction techniques to mitigate the potential problems(other than mitre joints), rather than go to elaborate efforts afterwards.

For example, I wonder if a very deep rabbet joint, with maybe just 1/16" to 1/8" of material remaining on the outside piece would show less than a standard **** joint, since it the joint is very near the corner and the glue would likely permeate that narrow section quite well. Obviously a narrow lip like this would be very easy to break off, so that would certainly be a potential drawback.

Also, rather than doing roundovers, might one do chamfers and place the chamfer edge right on the seam. Might that mask the effect of expansion?

Is the amount of expansion changed by the surface hardness of the mdf? Could it be sanded to remove the harder layer at the surface and in that way reduce the potential expansion?

I think this kind of construction technique options might be a good addition to your testing of treatments, if you are interested in exploring them. It just seems to make sense to try and address the problem at the source rather than treat it afterward. A combination of a change in construction techniques and simple seam treatment may offer the easiest solution.

BTW, how did you do the trenches?

Jim Holtz puts a layer of 1/8" MDF over the whole side panel which would be just about the same thing as a deep rabbit joint. The rabbit would be simpler if you don't break it.This would put the seam on the round over and probably would make it a little more difficult to see.

I definitely think if you can get away from this joint all together would be the best method. Problem is most builders drawings are designed with this type of joint. If one of the methods work it would be possible for someone to redo an existing finish if they don't like the seam showing.

A simple shallow v groove on the seam would do it also and wouldn't look bad.

As far as the trenching goes I just did it on my table belt sander. Would be nice to find a router bit to do it with. I just haven't looked into that yet.
Dave

[CokewithLime]

Re: Best methods for finishing MDF

I'm dying to try one of those, tho I wonder if it works well with MDF and how you have to adjust your measurements accordingly.

I have mostly used it on solid stock and BB ply but there should be no difference on setup for MDF. just a lot more dust...

A long as you have a good router table/fence and are working with consistent panel thickness these bits are very easy to set up and use.

First put matching witness marks on the outsides of the panels to be joined (just to keep insides/outsides identified) then set the depth of cut using a matching thickness piece of scrap to the same final material you are using.

Actually have a look at this set up PDF - pictures save a lot of words.....

[skatz]

Re: Best methods for finishing MDF

"That and I am sensitized to epoxy, so if I don't were full protection I get what is like poison ivy mixed with sun burn with lots of swelling. The only way to get ride of it taking steroid dose packets. Not fun, so I try to stay away from it as much as possible. Anyone can become sensitized to epoxy at any time, so becarefull. One you are sensitized its for life.
Dave[/QUOTE]"

Yikes, thats a full blown hypersensitivity reaction, potentially lethal. I'd stay away from anything that could set it off, including testing it for this forum!! Your airway could go into bronchospasm, and your goose, as they say, would be cooked unless you happen to have ready access to an epi-pen.

[evilskillit]

Re: Best methods for finishing MDF

I'm dying to try one of those, tho I wonder if it works well with MDF and how you have to adjust your measurements accordingly. Seems like it would be really nice, make squaring up the corners a bit easier.

[Ryan_M]

Re: Best methods for finishing MDF

Once I get some dust collection figured out for my router table I'm going to pick up one of those bits. Not just for hiding seams bit it looks like it will help a lot for alignment during glue-ups as well.

[CokewithLime]

Re: Best methods for finishing MDF

Has anyone tried using a 45 degree lock mitre bit


I have use these for years with great success in furniture construction - even works very well with most plywoods