Lock Mitre

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harryc

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Hi all,

I am thinking of making a couple of boxes and toying with the idea of getting a lock mitre router cutter to joint the sides.

Anybody any experience with these cutters

Harry
 
They are dreadful to set up. One suggestion made to me was to keep a sample of previous jobs to adjust the height/fence to in future.
I also find that keeping to a number a specified timber thicknesses helps as one you have the setting for a given thickness you can reproduce them accurately with a height gauge.

Roy.
 
One of the issues with this joint is that whilst one piece can be laid flat on the router table, the other has to be passed through on edge, this is quite a tricky operation and requires quite a tall fence.
 
Digit":m00ckqj1 said:
They are dreadful to set up. One suggestion made to me was to keep a sample of previous jobs to adjust the height/fence to in future.
I also find that keeping to a number a specified timber thicknesses helps as one you have the setting for a given thickness you can reproduce them accurately with a height gauge.

Roy.

When I bought my set of bits they came with set up blocks.
 
Thanks guys, might just give it a try out of curiosity.

Harry
 
Although I have not used mine for a while, a few years ago I used it extensively with great results.
I would like to add a tip when using a Lock Mitre, put a false fence in place to reduce the cut when shaping, it makes for a better finish and the job is so much easier all round, nine mm. is ideal as a set off, then remove and cut to the full depth.
Derek.
 
If you're determined to try them Harry for better or worse I'll tell of my experience.
Unfortunately this last couple of years I seem to have been making nothing but bloody great doors, wardrobes, kitchens, you get the picture?
Prior to that it was boxes, clocks and small items and I used lock mitres a lot. For such things as boxes and small draws they produce a beautiful clean mitred corner, but I found that the conventional router table was less than ideal.
The conventional router table has two problems with lock mitres,
one, you need a tall fence when cutting one half of the joint.
two, as the last cut is being made controlling the timber is very difficult as it is passing the cutter balanced on a knife edge!
I have found two ways around these problems,
one, I made a small vice mounted router table which could be turned so that the timber was always running horizontally.
Two, I inserted an alloy lined slot in to each 'fence' and used a sled, this removed the difficulty of balancing the timber on a knife edge at the last cut.
Unfortunately I can show no pics as the 'cheapo' router eventually burnt out and I dumped the lot with the intention of a MK11 to follow.
I also made a depth micrometer from a damaged Mic so the the cuts could be done in stages.
It also pays to make the timber wider than the final size as a means of removing any 'break out.'
Hope this helps, sounds a lot of work but if you are into boxes etc it's well worth the effort for the finished result.

Roy.
 
Roy thanks for the tip on keeping the piece of timber thicker to clean up any breakout. BTW I am only making a couple of boxes, but can not resist the temptation to try out a new toy

John they seem to vary from £20-30 for the Rutlands, Axminster up to £80 for the CMT, Freud.

Harry
 
May not be what you want, but the jig for splining mitres that is featured in one of Robert Wearing's books works a treat, and costs next to nothing to make.
I'd often wondered about mitre lock cutters, but always been too cheapskate to buy one. Now I've made up the Wearing jig, don't see the need for special cutter any more, as the resulting splined mitre must be at least as strong, if not better.
 
I had a solid cutter for my spindle shaper to make this cut; it's a terrific joint, with lots of gluing surface but as Roy notes it can be tedious to set up.

Of course, once set up you can run miles of material, so it's probably more suited to a production situation than a small shop doing custom work.
 
I have used these cutters extensively for making carriage clock cases.
They give a more professional finished article than using a solid block of wood with an insert hole drilled into it.

You have to realize that these cutters are just one option to solve a jointing exercise.

Would you use these cutters to join 25 m thick, 800mmlong x 400mm wide?
Probably not, biscuit jointers, loose tenons, dowels, dovetail joints, etc spring to mind for these sizes.

The surface area that is removed by these cutters, make it a safety issue, especially with the 1/4 inch shank cutters. You also need to remove the stock in one pass, so adjustment isn't a realistic option.

I have found that for drawers, boxes and clocks they are ok, because of the stock thickness it isn't an issue.
You can even cut with the wood grain against a fence with feather boards in place.

You have to take time setting up, but once set away you go.
You should also remember that the stock you pass through these cutters must be square, and be the same thickness....if not you will never get the pieces to join together.
 
I have used one of these in the past on veneered MDF, usually corners of desks for shop fits. Never used it in the router table but used free hand with a jig as they have been large sheets of MDF. The results are good, usually a little bit of breakout of the veneer as I've often had to go against the grain, but very accurate if you have the patience to set it up, veneer is only 0.6mm thick!
With solid timber I can imagine you could get a very good result, especially if you have the time to play with the setting to get the height right.

Johnny B
 
I cracked all the problems of machining when using them DT with a specially made router table so that I could make several passes.
But yes, the stock must be all the same size, I thicknessed all stock at the same time otherwise as you say the results look awful.
By sticking to a limited number of stock thicknesses the problems of setting up can be eased, but getting the first lot of settings is a pain!

Roy.
 
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