Lock Miter Bits

[James White]

Hi All,

I am having some trouble with a Porter Cable 43503PC Lock Miter bit. I am able to get the set up to were the miters will match up but there is no "lock" per say. In other words there is nothing preventing the miter from sliding out of alignment during glue up. It looks like it may be a manufacturing defect. However I just wanted to check with the Creek.

The tongue is substantially smaller than the grove. This allows a bit more than 1/16" of play. Is this normal for a lock miter bit? I have my doubts about that. It would defeat the purpose of even using a lock miter. Same as if it were a regular miter.

I have contacted PC and they said there are not set up instructions and couldn't even recommend what RPM to run it at. To there credit they are sending me a new one in case it is defective. But could not advise weather my results were normal or not.

Can anyone advise if they have used this bit or for that mater lock miter bits in general? By the way a am using to make some "Stickley Legs" QS on three sides.

James

[Rod Sheridan]

Hi James, I presume you are running one edge with the piece flat on the router table, and the other edge with the piece flat against the fence?

I've never used a router bit, however I use that cutter style for exactly what you're doing, and there is zero slop in the completed joint.

Regards, Rod.

[Alan Schwabacher]

If you are running with multiple passes, and there is a chance the stock might have shifted, that could mess up the cut. The thin edge is not likely strong enough to guide the piece against the fence for a final trim cut with the workpiece vertical. If you need to do that for a clean cut, clamp a straightedge to the workpiece to ride along the top of the fence.

If your fence is not square to the table, it would screw up the fit. If you are using a collet extender to get the bit above the table and that's causing the bit to wobble, that could not only mess up the cut, but would run the risk of messing you up pretty thoroughly.

But if everything is square and the workpieces are well controlled, a poor fit might indicate a defective bit.

[Jeff Bratt]

Setup instructions are the same for any brand...

http://www.infinitytools.com/pdf/lockmitre.pdf
http://www.leevalley.com/shopping/In...s.aspx?p=51601

Something is not right - the pieces should lock tightly together. Make sure you use featherboards - any deviation from a straight cut and the pieces may not fit together well. You also need to be careful with setup, as the entire edge that runs against the fence is routed away... some sort of fixturing is often required.

The bit height varies depending on the stock thickness. Once you get it setup correctly, make a couple small setup blocks so you can quickly set the correct bit height and fence position when you use the same stock in the future.

[James White]

Thank you for your replies. It looks like the bit is either defective or poor design. The tongue and grove portions of the bit are different by about .050" as best I can measure. I am using good technique as advised with feather boards. I am able to get good consistent results (no wobbles). But this bit will not produce anything that will "lock".

If you look at this link fig 4. http://www.leevalley.com/shopping/In...s.aspx?p=51601
I can produce all three conditions when the bit is set up properly. Hopefully the one PC is sending will be correct. It would be nice if a list member pops up to say they have this bit and it works properly.

James

[Joe Scharle]

I got one from MLCS a few months ago and it works as advertised. It does sound like the bit from what you say.

[David DeCristoforo]

Here's a "pretty simple" method for setting up the lock miter bit/cutter:

http://www.daviddecristoforo.com/Misc/lockmiter.pdf

Once you get the cutter "dialed in", mill all of your stock 1/16" thicker that the pieces you used for the setup. When you run the pieces, the extra 1/16" will provide a small "flat" so that you are not trying to run your stock on the "long point" of the miter which will be very weak and prone to chipping. After you mill your joints, plane down the stock to final dimension and you will have a nice sharp point.

[Rick Gooden]

Give this method a try: http://www.woodshopdemos.com/cmt-lm5.htm

[Chris Tsutsui]

A long time ago I've assembled lock mitered boxes before. Setup of the bit was trial and error on small scrap pieces of the stock which was 3/4" maple laminated MDF...

Once setup right, the edge would be nice and crisp and the edges easily lock without play.

But after you brush the edges with wood glue, you'll still need to use clamps to get everything perfect.

One art project had lock miters for a box in the shape of a pyramid, so the use of "C" shaped spring load miter clamps worked ok. Use steam to pop out the indentations after the glue is set.

After you achieve that sharp edge, I like to take a burnisher such as a block of nylon/plastic and run it along the edge. This will push the two edges together if there are any tiny gaps. Nobody likes a splinter or to get cut on a super sharp edge. (If you use sand paper then the gap will still be there.)

[James White]

I am not have trouble setting up the bit. It is simply a problem with the bit. Either it is a poor design that allows the slop. Or it is a defective bit. I am hoping for the later. I'll be sure to let you all know when the new bit arrives.

Joe,

Do you have the Porter Cable 43503PC Lock Miter bit?

David,

That is an excellent tip. I was thinking I could leave some meat on the edge and then joint/plane the post after glue up. But I like your idea better.

James

[Jay Jeffery]

It seems Black and Decker don't do a very good job of supporting their products, or at least the Porter-Cable ones. I wanted to make some boxes out of 3/8" material with a lock miter bit. I found a good deal on the Porter Cable bit, but couldn't find the stock thickness range it was designed for. I scoured the internet, posted on some forums, called the retailer, emailed Porter-Cable and even talked to someone at Porter-Cable on the phone. Nobody could tell me. I ordered the bit anyway and it was printed right there on the front of the package: 3/8-3/4" thick material. Very unimpressive.

But hey, you got a free bit out of them. That's kind of cool.

[Joe Scharle]

Joe,

Do you have the Porter Cable 43503PC Lock Miter bit?

No, I tend to use MLCS, Freud, CMT and Whiteside. And there's a Woodcraft nearby.

[James White]

Well this turned out to be a heck of a journey. I waited two weeks for PC/Dewalt to send the replacement bit and nothing showed up. I knew that it was too good to be true!

So I called them back and they said I did not get it yet because it was never sent out. So I ask why. Well it looks like we were out of stock and it is now discontinued. Ok so what can we do. Let me see if one of the local service centers has one. Your in luck one of the centers in MA has one. Thats a 1.5 hr drive for me. Will they ship it. I don't know call them and ask. Ill send them an email letting them know you will call.

Called them and after two calls I was able to get a hold of the manager. Says I need to send him the old bit first. Wait a week for the return shipping label and nothing arrived. Call back and was told they will send another. Comes in three days and I send the old bit to them and a new bit shows up in another three days. Great now I can finish my project.

Set it up and low and behold. This time the tung is too big for the grove. The first bit was the other way around the grove was too big for the tung causing slop.

Back on the phone with PC/dewalt and they don't know what to do. I'm thinking if two out of two bits were bad and they are discontinued there must have been "issues" with the manufacure of this bit. So I suggest they send me the 43514PC This is a 3/4" max capacity bit were the original was up to 1-3/16" and it retails for about half of the big bit.

Today I tested the bit and nailed the setup on the second piece of scrap. So I have a bit with less capacity. But it works!

James

[Anthony Whitesell]

Pictures are worth a thousand words. Any chances of putting up a few for those that have survived the learning curve to take a look at and provide some more feed back.

[John Lucas]

James,
It sounds like you are in business. Let me add one point. Once you have everything set up right, use a holddown or block to run the vertical piece. If there is any vibration your joint willl show it. Also, run the vertical piece several times. As long as it sounds like it is cutting, make additional passes.
Locking miter a favorite bit of mine. I use CMT but I am sure yours is the same. I am 6 miles south of providence...sounds like you might be close enough t0 stop in. Let me know if that would help.