Dovetail by router problem cropping up...

[dbhost]

I am thinking this has to do with bit speed, because it simply seems to be cutting too fast, but I haven't slowed the router down to find out...

I seem to be blowing out the back side of the tails when I cut them. I have been following the MLCS instructions which simply say to follow the template with the guide bushing, sort of like drawing the router around, but I am thinking possibly about going in on the left side, coming out the same way, and finishing the cut by going on on the right side instead of going in on the left, and drawing around to come out on the right...

Does any of this make sense?

BTW, I am cutting dovetails in solid Ponderosa Pine scrap that has been in the shop at least 6 years. I am trying to build some little boxes for LOML's desk...

[tfischer]

I'm far from an expert, but I've essentially done what you said and it does avoid tearout. Similarly, you can go across the width between each 'finger' first and get the same effect.

-Tim

[dbhost]

I'm far from an expert, but I've essentially done what you said and it does avoid tearout. Similarly, you can go across the width between each 'finger' first and get the same effect.

-Tim

So instead of going in full depth, kind of nibble away between the fingers, say for the first 1/4" or so of the cut? That would make sense... I have the jig set up and am ready to start cutting when I get home tonight. I'll try that...

These are the first DTs I have cut with the Hitachi, and I think I will be very glad for the variable speed adjustment.

[LCHIEN]

My suggestion, go left to right.
Make a number of passes in which you cut smaller bites, you can initially move faster across the outer ends of the fingers, and make slower passes as you go deepr into the fingers, always taking smaller bites, you don't have to control the position of the router as the template will prevent overcutting, just tkae off what comes off easily and then finally make a finishing pass in whihc you follow the template quite closely by then you should be taking off very small amounts and hear the zzzt as it does the cutting.

[dbhost]

Yeah, kind of what I was figuring. This is the first time I have had a DT blowout. But then again, all my other DTs were cut with the old Ryobi R161 1.5 HP router. Not quite the same machine...

[RayintheUK]

Use a scrap backing board. Totally eliminates tear-out IME.

Ray.

[Black wallnut]

Which jig are you using?

[LarryG]

What Ray said, but also what MarK said. When you saying you're blowing out the back of the tails, I take this to mean the face of the board that is farthest away from you. If so, and if you're using a conventional DT jig and cutting through DTs, clamp a scrap board in the top clamp where the pin board would go if you were cutting half-blinds. The scrap will keep the back side from blowing out.

[dbhost]

Which jig are you using?

MLCS Pins & Tails template. The small one. I have been using the big one for a while, with no problem, using the old Ryobi router, the Hitachi is just too aggressive at full speed. I am home for lunch to try it out, I set it up, and tried a MUCH slower rpm on the router, and it cuts smooth as butter now with no tear out. And the tear out was happening on the area facing the operator when cutting. I simply slowed the router down and nibbled in on both edges first, then went all the way through.

Nice, good fitting DTs with no tearout now.

I have had this template setup for a while now, but my original mount block wasn't quite what the MFG called for, so I built blocks to their specs and went through the setup again... I am ready to go grab some real wood and get to building a shadow box for LOML to keep her wedding bouquet in. Her b-day is coming up you know...

[Black wallnut]

To lessen tear out you could also try at leat 2 other things. 1) try a light pass as a climb cut to start, that is left to right. 2) clamp a thin piece of scrap on top of the board you are cutting and cut through it thus making a zero clearence sacraficial backer board or actually a fronter board since it will be facing you.

All that said if slowing the cutter down works for ya I do not see any problem with that as long as you are not getting burning or feeding too fast, stressing the bit.

[dbhost]

I think I'm good with it now...

No burning, or anything like that. The speed at which the waste is expelled now is roughly equal to when I used the Ryobi. I have no idea if the Hitachi really is that much faster, but it certainly seems like it...

[JimD]

I've never tried a slower speed, maybe I will sometime.

Right to left if back-cutting, however, to reduce splintering/chipout. Left to right is normal cutting. Maybe I wasn't reading closely enough bit it seems like somebody posted it the other way. (my directions are with me facing the jig).

Jim

[dbhost]

Okay, it works fine at the slower speed in the older pine, but bought today BORG white pine and we are back to tearout. I have plenty enough scrap that I am going to try the sacrificial strip approach to make this work without tearout... See how that works...

[dbhost]

Okay, I have the process for the pins down pat. Now how the heck do I keep from tearing out the tails?

On the pins I just basically VERY lightly swipe back and forth left to right, pushing slightly back and nibbing away. I had to turn the router speed full up and do it this way...

Since the DT bit is larger diameter, I slowed it down a hair for the tails, (about one click, whatever speed that is, I figured larger diameter needed slower speed). Anyway, dovetailing a 12" board gives me 3 blown tails. I am going to cut up some new boards for the tails and try again this weekend. I have a late work day, and some Halloween stuff to do tonight and tomorrow...

I think it has a LOT to do with how aggressive I am with the router. I seem to have better luck just sort of setting the bit against the work piece and letting it nibble away, but I am worried about burning the piece... I haven't tried the sacrifical strip yet...

[poolhound]

I am not sure that a slower bit speed is the answer. Having just got my Leigh DT jig, it reccomended using the highest speed possible. To reduce tearout, climb cutting and backerboards are the way to go - IMHO.