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Massive Tearout on Homemade BoxJoint Jig

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Anonymous

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Hi all :)

I have one of those "Timelife" woodworking books & in there is a really great boxjoint jig or comb joint whatever you choose to call it.

Well I spent ages making the jig & it looks very nice, with a little micro adjusting system which works very well indeed, however my first few goes of the jig are less inspiring.

Im using a 1/4" straight cutter (wealdon) & im making 1/4" comb joints, now unless im mistake (quite possible) you have to use these jigs very much like dovetail jigs, ie do the cut all in one pass, so being as I dont like taking that much meat off in one pass im feeding it in very slowly.

Ok so I get my drawer side (10mm ply or mdf) & hold it up against the jig, I run through with a starting cut then this fits over the pin which is a guide for the next cut, well you know how it works so I will get onto the problem, as I push the jig along on the router table slot, as the cutter starts cutting the wood, it tends to rip out, I slowly push the jig through cutting more into the wood & it can rip out so much on the front of my drawer side that the little comb joints being made can actually get broken, as the cutter completes the cut & exits out the rear breakout isnt a problem as the jig has a removable backing piece, which does a good job of stopping tear out, but its the front thats causing the problem,

Ive tried a piece of beech & its perfect, no problems at all, but im wanting my drawer sides & back etc.. to be made out of plywood, or MDF with a false front made from a nice hardwood.

Surely you can make comb joints in MDF without all this hassle??? Plywood as it breaks out you can find yourself with a nice fitting joint but where the cutter started to cut its ripped out a chunk of the ply, like a whole layer removed, with MDF its more like a ragged edge & at worst part of the little fingers broken.

I can cure the problem by taking smaller depth of cuts, like 2mm at a time but this involves raising & lowering the cutter height, ive got a RoutRLift so its only a turn of the handle, but the cutter height has to be very accurate as this dictates how well the joint fits together at the end, so I feel its wrong to keep altering the height.

Anybody have any ideas as to whats going wrong? if ive not explained it enough or you need any more details please let me know & I will try & explain clearer.
 

Philly

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Hi NIck,
Welcome to the forum!
Tearout is really annoying, spoiling a great looking result. Have you tried putting a piece of "waste" mdf infront and/or behind the piece your cutting? That normally works for me. You might have to use a fresh scrap each time, but hey, you can't beat a perfect result!
best regards
Philly :D
 

SimonA

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I would have to go with Philly's suggestion to be honest Nick.....just wack a bit of scrap on the front and bobs your uncle.......or is he you ant'...hmmm
:lol:

SimonA
 

Alf

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Welcome to the forum, Nick.

Ply and MDF suffer terribly from this sort of problem. As Philly and Si have said, scrap backing pieces are the thing to try. Good luck with it.

Cheers, Alf
 

Steve Maskery

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Hear here.
This kind of problem is often found on commercial dovetaile jigs too. A backup piece is a MUST. It will solve 99% of your problems. Of course the manufactureres never tell you that, but we, bless our little hearts, will.
Best of luck and keep tryng.
Cheers
Steve
 

Rattie

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Hi Nick,

Like what they all said...

Nick_C":4cmgddqv said:
now unless im mistake (quite possible) you have to use these jigs very much like dovetail jigs, ie do the cut all in one pass, so being as I dont like taking that much meat off in one pass im feeding it in very slowly.
Well not really. The thing with dovetail jigs is that you have to cut the PINS in one pass, i.e. the cuts done with the dovetail cutter. The actual tails which you cut with a straight cutter you can fanny about as much as necessary to get the perfect fit.

Mapping that onto box joints where again you're using a straight bit, you can use multiple passes. Where this gets useful, is where you use a narrower bit, and do a climbing cut to finish off the high breakout edges. That is where after taking out the bulk of the stock in the normal direction, you take the last whisker off with the router moving in the self-feeding DANGEROUS direction. Of course with a narrow bit removing a tiny amount of stock it's more controllable than normal. In conjunction with a back piece on either side of the cut, this can help redice breakout.

I don't know about box joints in MDF (though it seems futile, what with MDF having such dull end grain :wink:) but cheap ply is terrible for breakout. You might want to track down some better stock. The thicker the face ply generally the better behaved it is YMMV.

Hope something in there helps, late now, zzzz

Martyn
 

Midnight

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Only other ideas I can think of would be to pre-score through the ply with a good sharp knife, or give up the ply box joint in favor of a drawer lock joint...
 

devonwoody

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My Triton outfit for finger cutting has a special router bit, the blades have a designed serated edge(no jokes please) .
There are two cutting edges like a normal straight cutter but a notch every 1/4" or so along the blade. Perhaps it helps clear out.
However mdf was still a bit ropey the last time I used the cutter.
 
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Anonymous

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Nick

I would think that you could take seveal shallow passes as long as the location pin is not too high - I can on my home made finger jig which I guess is similar to yours. (it's on here somewhere)

For my Leigh dovetail jig, I put some thin ply in front and behind for expensive wood to prevent breakout
 

Johnboy

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This doesn't help with the original question but for MDF or Ply carcases to be fitted with a false front I just biscuit the sides to the front/back. Plenty strong enough IMHO.

John
 

Aragorn

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Welcome to the forums Nick
Box joints in MDF :!: :?: :shock: Now I've heard it all!
Can't imagine glorified cardboard would rout well into a joint box.
Plywood might be OK if using the cabinet grade stuff. The laminations could look quite nice as "end grain".
The rule for tear out is to back it up - front, back, sideways ... wherever.
If the back up is incorporated into the jig itself, you won't need to change it during the job as it will always be in the correct relative position to the cutter.
 
A

Anonymous

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First of all, thanks to everyone who replied, its good of you all to take the time to help out... :wink:

From what you have all said it seems the general idea is to have a front backing piece as well as the back, I must say I did try this but only by holding a piece of hardboard in front of the drawer to be box jointed, all in all it was all too hard to hold both pieces, so im going to try & modify the jig so I can use some clamps, I will then clamp the drawer side & a front piece of wood to prevent the breakout.

Yep I guess box joints on MDF isnt the norm, but I mainly want them due to the ease of assembly, last time I made a drawer it was hard to clamp it all up with butt joints, although I do have a band clamp now which makes it a LOT easier! but these box joints hold together nicely when done right.

I will get there in the end (im sure I will, I hope I will) :p

Anyway, thanks again everyone, you have all been very helpful, ive got plenty more ideas now...
 

johnelliott

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If you go up to 15mm board thickness, you can use pocket screws to secure the corners, no box joints or dovetails needed, or clamps, just simple butt joints secured by three screws at each corner. It would work even better with birch plywood which takes screws better
John
 
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