Strengthening MDF edges/corners for jigs

[transatlantic]

Do the MDF sealers you see around like 'Rustins Quick Drying MDF Sealer Clear' do anything for strengthening the corners where it always comes apart like cardboard? I like to use MDF for jigs as it's cheap and easily avaliable, but it always ends up fraying at the edges/corners which ruins the accuracy of the jig.

Ideally, I'd use birch plywood, but I can't justify the cost for jigs and avaliability is difficult.

I also use stuff like 'Wickes Non Structural Hardwood Plywood' but I find it's full of voids and often very uneven. You often see overlaping plys which create bumps, so not great for accurate jigs.

Hardwood Plywood => Easily avaliable, strong, inconsistent thickness, good edges
MDF => Easily avaliable, relatively strong, very consistent thickness, weak edges
Chipboard=> Easily avaliable, relatively weak, very consistent thickness, weak edges

 

[tomatwark]

When I am on site and a bathroom is being done, I normally collect the off cuts of multipanel wet wall if it is being used, it makes great jig material.

 

[iNewbie]

Some guitar builders use (slightly watered down) Titebond glue,......or Superglue, to add some strength.

 

[Peter Sefton]

I have found cellulose sanding sealer the best thing for the edges of MDF, although I use it more on laminate jig making and only on short runs for machine jigs.

Cheers Peter

 

[petermillard]

Use MR MDF if you can - much better board for not much more money. Also 'wood hardener' will toughen up the edges quite well - probably similar to Peter Sefton's cellulose sealer mentioned above.

HTH P

 

[Paul Chapman]

I always lip the edges of MDF with solid wood. That way the jigs last for ages.

Cheers

Paul

 

[Sgian Dubh]

Rubbing or brushing neat epoxy resin to the edge is another means to strengthen them. That's the resin alone without the use of thickeners or other bulking agents. Brand names such as West System, available from Axminster spring to mind, as well as suppliers such as these people: http://www.easycomposites.co.uk/#!/ Slainte.

 

[Mr T]

Bite the bullet and use birch ply, for the size of most jigs the difference in price will only be pence. BP takes screws better and is nicer to handle.

Chris

 

[Rorschach]

I have used superglue to repair exposed MDF edges so I see no reason it won't work as a preventative measure.

 

[woodbrains]

Hello,

I agree with Mr T. The whole point in a jig is that it will be a tool that will last for years and be used a lot. I don't think you can justify using MDF for them. By the time you mess about with dodges and fixes to try and overcome the shortfalls in the mdf, and perhaps get 10% longer life out of the jig, only to have to build again, you may as well use the right material initially and get on with some woodwork! You can get an awful lot of jigs out if a sheet of 18mm birch ply, how does the price of that compare to a sheet of MRMDF and a tin of sealer?

Mike.

 

[transatlantic]

Bite the bullet and use birch ply, for the size of most jigs the difference in price will only be pence. BP takes screws better and is nicer to handle.

Chris

It's certainly not pence for me. MDF I can get in my local Timber merchant, £25 for a full sheet cut into manageable sized pieces. Birch ply I have to get delivered ordered online, which is like £60 a sheet plus the extortionate delivery price.

 

[Superstrat]

How about trying Softwood Plywood from somewhere like B&Q (http://www.diy.com/departments/plywood-plywood-th18mm-w1220mm-l2440mm-1/945875_BQ.prd)? I've used it to make shop furniture, it's no way the quality of birch ply buy you may find it's a reasonable compromise.

A 2440x1220x18 board is £33 (5 or more sheets = £27 each) and, apart from a few knot repairs, it doesn't have the problems you describe with hardwood plywood which is dreadful stuff.

They also sell these at 2440x607x18.

 

[transatlantic]

How about trying Softwood Plywood from somewhere like B&Q (http://www.diy.com/departments/plywood-plywood-th18mm-w1220mm-l2440mm-1/945875_BQ.prd)? I've used it to make shop furniture, it's no way the quality of birch ply buy you may find it's a reasonable compromise.

A 2440x1220x18 board is £33 (5 or more sheets = £27 each) and, apart from a few knot repairs, it doesn't have the problems you describe with hardwood plywood which is dreadful stuff.

They also sell these at 2440x607x18.

I'll take a look when I next go down, but I have always found that stuff to look worse than the hardwood plywood?

 

[Superstrat]

How about trying Softwood Plywood from somewhere like B&Q (http://www.diy.com/departments/plywood-plywood-th18mm-w1220mm-l2440mm-1/945875_BQ.prd)? I've used it to make shop furniture, it's no way the quality of birch ply buy you may find it's a reasonable compromise.

A 2440x1220x18 board is £33 (5 or more sheets = £27 each) and, apart from a few knot repairs, it doesn't have the problems you describe with hardwood plywood which is dreadful stuff.

They also sell these at 2440x607x18.

I'll take a look when I next go down, but I have always found that stuff to look worse than the hardwood plywood?

Maybe I got lucky. I was going to order some more for a mitre saw station I want to build, think I'll take another look first too. They also do a product they call Spruce Plywood for the same price which I thought was the same so I'll check that out too. The hardwood plywood is really nasty but this stuff was really quite nice.

Good luck and let me know how you get on.

 

[ED65]

...but I have always found that stuff to look worse than the hardwood plywood?

Me too, dreadful stuff usually when I see it. MDF isn't without its faults but IME even the cheap stuff is reasonably consistent and durable.

FWIW I don't find the edges particularly prone to damage when used for jigs and such, but if needed they can be strengthened with any finish or glue as advised above, even hide glue will do wonders. Thinned varnish would be my go-to for this type of thing since it can be so cheap, but if I had some spare 3-min epoxy to hand I wouldn't be averse to using that as it's extra tough.

 

[Superstrat]

Just checked back over my B&Q receipts. This is exactly what I bought last June...

http://www.diy.com/departments/plywood-sheet-th18mm-w607mm-l2440mm-1/1420305_BQ.prd

Here's the detail from my receipt, as you can see I bought 3 sheets at £16 each...

SOFTWOOD PLY 2440X607X18MM 3663602055945 3 £48.00

It really was as good as that shown on their photo. I bought these smaller sheets so I could get them in the car but I was going to have five full sheets delivered. I'll eyeball them first though, in case the quality has changed.

 

[Sgian Dubh]

The whole point in a jig is that it will be a tool that will last for years and be used a lot. I don't think you can justify using MDF for them. Mike.

I don't think it's always quite that simple Mike. Whilst I agree with both you and Chris that birch ply does have better edge strength that will stand many repeated uses, it's not always the case that a pattern has to be durable enough to give years of frequent repeated services . For instance, if only four, eight, ten or perhaps twenty repeats are required then an MDF pattern is usually more than adequate, as I can testify from experience. Additionally, if you're shaping that edge by hand with spokeshaves and the like, MDF is far easier to manipulate with such tools than plywood - the lack of grain direction and relative softness are advantageous here. And finally, you can use the pattern created in MDF on a one-off basis to make a more durable edged repeat pattern in a different material such as the aforementioned plywood, or anything else that's preferred, e.g., aluminium, solid surface material (Corian for example) and so on.

We could all, I suppose, go a stage further and do away with most of these jigs, patterns and formers, i.e., knock out a drawing in AutoCAD and put the job on a CNC machine - but probably best not go there ... ha, ha. Slainte.

 

[transatlantic]

Just checked back over my B&Q receipts. This is exactly what I bought last June...

http://www.diy.com/departments/plywood-sheet-th18mm-w607mm-l2440mm-1/1420305_BQ.prd

Here's the detail from my receipt, as you can see I bought 3 sheets at £16 each...

SOFTWOOD PLY 2440X607X18MM 3663602055945 3 £48.00

It really was as good as that shown on their photo. I bought these smaller sheets so I could get them in the car but I was going to have five full sheets delivered. I'll eyeball them first though, in case the quality has changed.

Thanks. Will definitely take a look then. When you mentioned it, I was thinking of spruce ply, which looks awful, even on their site.

 

[Superstrat]

I see that Wickes seems to be selling a very similar product i.e. softwood plywood. Cheaper too for smaller quantities of the full 8x4 sheets. They have 15% discount on top for this weekend as well. I don't know what the quality is like though but may also be worth a look if you're passing.

 

[woodbrains]

The whole point in a jig is that it will be a tool that will last for years and be used a lot. I don't think you can justify using MDF for them. Mike.

I don't think it's always quite that simple Mike. Whilst I agree with both you and Chris that birch ply does have better edge strength that will stand many repeated uses, it's not always the case that a pattern has to be durable enough to give years of frequent repeated services . For instance, if only four, eight, ten or perhaps twenty repeats are required then an MDF pattern is usually more than adequate, as I can testify from experience. Additionally, if you're shaping that edge by hand with spokeshaves and the like, MDF is far easier to manipulate with such tools than plywood - the lack of grain direction and relative softness are advantageous here. And finally, you can use the pattern created in MDF on a one-off basis to make a more durable edged repeat pattern in a different material such as the aforementioned plywood, or anything else that's preferred, e.g., aluminium, solid surface material (Corian for example) and so on.

Hello,

I agree that sometimes we just need something to pattern route around for a short run, but then there is no real problem with edge splitting. Coating with West System epoxy might end up a wee bit more expensive than making from ply, though. However, when building jigs that are made from multiple parts that need glue and screw construction, MDF sucks wind. So it is horses for courses. I wouldn't make something like a crosscut sled or tenoning jig for the TS from MDF as I'd want those to last. For that matter, these plus a housing jig for the router, drill press top table, shooting board etc. could all probably come out of one 8 by 4 sheet of birch ply, made to last indefinitely. It would be a great investment, and I wouldn't want to spend the time to remake over. My most used jigs are made from Trespa, but I wasn't going to suggest that!

Mike.