Leigh Jig dovetails tearing out

[dan lemkin]

I have a 24" superjig and am new to using it. I have made about 6 boxes... The fit and finish of the work is fine... but when I am making through dovetails... both the dovetail and straight bit are tearing out on the rear of the boards as I feed through...

I feed it very slow and use a bosch var speed router at full speed. I have tried multiple different feed directions, but it still tears out. I am using hard maple, cherry, and rosewood.

The tearout are slivers about 1/16 to 1/8" wide and about the length of the tails. I tried putting some 1/4 luan behind it to provide a backing... it didn't prevent the tearout, but it did shread the luan...

Is this a technique issue? Are my bits dull? (relatively new) Any advice about how to reduce?

[george wilson]

I haven't used that jig,but I'd suggest that Luan is not strong enough to contain the tear outs. You probably need to use a hardwood backer. How sharp is your router bit??? If it is carbide,try a HSS one. High speed steel is sharper than carbide,at least in any of the grinding techniques used on router bits.

[Scott Mann]

I had similar issues when using my Rockler jig. I started using blue painters tape on both faces of the board and have not had any issues since. I still use a backer board, but i use MDF.

[Tom Leasure]

I have a 24" superjig and am new to using it. I have made about 6 boxes... The fit and finish of the work is fine... but when I am making through dovetails... both the dovetail and straight bit are tearing out on the rear of the boards as I feed through...

I feed it very slow and use a bosch var speed router at full speed. I have tried multiple different feed directions, but it still tears out. I am using hard maple, cherry, and rosewood.

The tearout are slivers about 1/16 to 1/8" wide and about the length of the tails. I tried putting some 1/4 luan behind it to provide a backing... it didn't prevent the tearout, but it did shread the luan...

Is this a technique issue? Are my bits dull? (relatively new) Any advice about how to reduce?


Use a piece of 1/2 to 3/4 scrap - tearout will cease
Tom

[Pat Smith]

Use a piece of 1/2 to 3/4 scrap - tearout will cease
Tom

Do you mean putting the scrap under the main work piece as backing or what?

[Karl Brogger]

Forget the backer. Even with a backer you will always get some tearout.

Just cut your fronts+backs, and sides taller. If I need a 3-7/8 tall drawer, I rough cut it at 4-3/8 and take a 1/4" off the top and bottom once I'm done routing it. You'll have to adjust your jig so for the extra 1/4" in height so you get the spacing you want on the drawer bottom.

[Jim Summers]

Forget the backer. Even with a backer you will always get some tearout.

Just cut your fronts+backs, and sides taller. If I need a 3-7/8 tall drawer, I rough cut it at 4-3/8 and take a 1/4" off the top and bottom once I'm done routing it. You'll have to adjust your jig so for the extra 1/4" in height so you get the spacing you want on the drawer bottom.


If it is the TO I have gotten with thru dovetails, the TO occurs down in the base of the joint or the bottom of the router bit. The last joints I made I scored the bottoms with a utility knife before cutting. It worked well. Takes a lot of time though. I am going to try the blue tape next time.

HTH

[Bob Wingard]

Are you using 1/4" shank bits ?? If so, try some 8mm or 1/2" if possible .. the bit chatter can cause a lot of what you describe.

[Jim Kountz]

If you score the baselines and use a proper backer board you will NOT get any tearout. If you still do, either your bits are dull or you technique just stinks! Sorry if that sounds rude but its the only was to say it really. I use a Leigh jig all the time and tearout is not a problem anymore using these suggestions.
Also pay close attention to the feed direction, going against the rotation goes a long way towards a smoother finish.

[Joe Scharle]

You didn't say, but your HB DTs probably look good because the proper backer board (an end) is in place and properly snugged up. Apply the same logic to your thru DTs and I think you'll be fine. You don't have to give the backer board a new face each cut because it shouldn't change position until you're done. As long as the exit of the cut receives full backing it cannot splinter. HSS works best, just keep then honed.

[Dewey Torres]

I agree with Jim...
Try it that way and see for yourself!

[Jim Tobias]

A 2nd to Jim, Joe and Dewey"s recommednation. I have a Leigh Jig and do what they are suggesting and get NO tearout. Proper backerboard material in the right place is the key. Also read the Leigh manual one more time about routing direction.

Jim

[Steve Rozmiarek]

Dan, the advice you've gotten on the backer boards is spot on, and they are critical. I like solid of whatever scrap is laying around, and change them periodically.

One more thing, it is possible to get tearout on the fronts as well, just remember to climb cut a light pass first, which does the same thing as the utility knife trick, just saving you an extra step. You only have to cut 1/16" deep or so to stop all front blowout on solid wood.

[Jim Kountz]

Yes indeedy Steve, I forgot about the very important climb cut first. Thats also a critical step for any DT jig.
Thanks for adding that one!!