Half Blind Dovetail - Pin Tearout - Router Forums
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post #1 of 10 (permalink) Old 03-11-2014, 02:48 PM Thread Starter
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Default Half Blind Dovetail - Pin Tearout

Newbie here trying to learn the hang of woodworking in general and table routing specifically...

So, my dilemma is in routing the pins for half blind dovetails I'm getting tearout and some chipping. Not consistently, but enough to show on the joint. I understand that it's an end grain cut, but doing them "face down" on a table doesn't give me any way to back them up like I can with the tails.

I'm building drawers sides with 1/2" poplar stock and I'm running a 1/2" 14 degree Whiteside dovetail bit set up with an Incra LS Positioner and Porter Cable 7518 motor. Router RPM is maxed out.

I've tried pushing the stock into the bit as slow as I can, but I can't seem to stop the bit from "grabbing" the stock and jerking it just enough to chip the outside of the pin cuts.

Any helpful advice from the experts out there? I'm thinking a featherboard would stop any side to side movement, but with a fence on one side, a featherboard on the other, and pushing the stock into the Incra ShopStop it seems like the stock is almost too trapped to be controlled safely if there's a kickback (I am using a handled push block). Plus, I'm not sure a featherboard is the answer because I don't think I could back out against the featherboard vanes too easily.
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post #2 of 10 (permalink) Old 03-11-2014, 11:15 PM
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Jt I don't see anything you're doing wrong but I agree with you I'm afraid the feather board would be a problem.
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post #3 of 10 (permalink) Old 03-11-2014, 11:46 PM
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post #4 of 10 (permalink) Old 03-12-2014, 09:23 AM
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I have had the same problem from time to time using the Incra Jig Ultra. Your idea to use a feather board is not off track, however I use a solid board to travel along side the pin board that I am just hand holding. I have one hand on the pin board well back from the cutting surface and the other hand is holding a board that is usually about 3/4 stock and it is longer than the pin board. This gives the side support against the bit pushing the pin board to the outside. The pin board cannot rise because you are holding it down. Unless you have an odd grain pattern in the wood this should stop the tearout. If you are using an Incra router table top, like I have, part of the problem is that the surface is so smooth and slippery it is easy to get just a slight movement to the side when passing over the bit. The board that travels along with the pin board will stop that. Give it a try and let us know.

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post #5 of 10 (permalink) Old 03-12-2014, 04:05 PM
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Default Leader board

Try placing a "leader board" (a piece of scrap stock) in front of the pin board; like a back up board only the converse. Hold both firmly against the fence and firmly together in the direction parallel to the fence. You can easily make a push block that will accomplish this; long enough to hold downward pressure on both of the boards that are being cut. Make it a bit narrower and put a lip on one edge to allow holding firm pressure against the fence. If that doesn't answer you may have a problem with the cutter.

Let us know when you find a solution - thanks

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post #6 of 10 (permalink) Old 03-13-2014, 03:06 PM Thread Starter
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Thanks for the tips everyone - I'll try the modified side support method with some scrap stock as mentioned and see if that helps.

The idea of a leaderboard sounds good, but I'm still having issues clearing the cut waste from the dovetail when making through cuts, like during the centering process. I'm even using the Incra clean sweep rings with the air slots and a 4" dust collector. For some reason the waste just jams up in the dovetail and has to be pried out when the cut is complete - I suppose that's a different subject for a different post though, lest I hijack my own thread...

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post #7 of 10 (permalink) Old 03-19-2014, 04:20 AM
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I have had the exact same problem. I talked to Mark about it. I've tried tons of pressure, different supports, but in the end none of which helped. Here is what Mark had to say about it in an email to me:

"I've experienced what you're describing many times. There are several factors at work, but it's mostly the lumber's grain direction & density and the router bit.

Some bits will "self feed" more aggressively than others. There's not much you can do here short of changing bits, but for the pin cuts especially, run the router as fast as it will go. At lower RPM, the bit is taking bigger bites for a given feed rate, making the flutes dig in more instead of shaving off smaller bites.

To keep the leading end of the board from getting pulled sideways into the router bit opening by the bit's rotation, keep slight counter clockwise tension on the board while running it along the fence…if it pulls the board toward the stop, the cuts will usually be fine as long as long as the board is kept against the fence. Also keep a good coat of wax on the router table & fence surface and use a push block with a clean, tacky rubber bottom to get the best control over the lumber."

At the end of the day, none of it helped me. (and I will note that I've tried both Whiteside and Eagle America bits both of which usually work the best, and neither helped).

Unless I'm going to work in oak, cherry, cedar, or pine, I've given up with the Incra. Fortunately for me, I bought the positioner for the Tablesaw and added the router table and superfence to that. I plan on using the router table for all my table needs and using something else for my dovetails and box joints.

Last edited by wbrisett; 03-19-2014 at 04:23 AM.
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post #8 of 10 (permalink) Old 03-25-2014, 02:12 PM Thread Starter
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Thanks for the above advice. I cut another series of pins the other day and had much better luck by using the "side board" method. It may not cure the issue, but this set turned out pretty good so I'll stick with it. I'd sure hate to abandon the Incra for dovetails since that was the capability that drew me to it most; I'm looking forward to trying some of the more complicated joints soon like the double dovetail.

And something else I learned was to run the through cuts (like drawer grooves) back through the router for a 2nd pass to remove all the trapped cut waste. (Just make sure you haven't turned the piece around before you do it - ask me how I know this.... haha).
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post #9 of 10 (permalink) Old 04-02-2014, 12:31 PM
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Default More tips

Hi, all-

I should probably first qualify a comment I made earlier - "I've experienced what you're describing many times." Yes, for sure, but it's not been frequent across the 10,000+ corner joints that I've routed with Incra systems. I'd say that significant self-feeding or minor chip out only affects about 5% of the pin cuts.

This thread covers two mostly separate matters. They come up about twice a year in conversations with customers and they haven't posed problems for me personally, but I've been thinking of a few other possibilities since my conversation with Wayne beyond what's already been discussed.

Using a really sharp bit, tear out or chip out is largely a function of grain direction near the end of the board, as has been mentioned. I've never needed to deviate from the normal method, but if tear out is severe or consistent, you can leave the pin board a little long, rout the grooves between the pins longer to match, then cut the board to final length, taking the damaged end grain with it.

A leader board could be difficult to secure...I'd be wary of trying it. Also, I don't think it's the situation here, but cutting into edge grain will produce heinous tear out...I occasionally chat with customers want to join boards on their long edges instead of ends.

If a bit/lumber combination tends to self-feed, there are a few things I'd recommend to minimize it in addition to what was quoted above -

- If you're using a plunge router, make sure the plunge is locked up tight. The motor bouncing around on its posts will pull the lumber right out of your hands (I forgot once). If you have a midsize router that came with two bases, use the fixed base. The plunge bases on a number of these routers aren't stable enough for router table use.

- Wax the heck out of both the table top and the fence surface to get the best feed control, slicker is better. The enemy is static friction...this is resistance to sliding while stationary, then suddenly breaking, free producing a rapid jerk/stop/jerk motion.

- More RPM is usually better, but I wouldn't say "always".

If you keep the lumber going straight if it wants to self-feed, it won't affect the accuracy of the cut. A few suggestions -

- Keep your right hand on the push block and your left hand near the trailing end of the board, keeping the trailing edge in solid contact with the fence. This helps counteract the clockwise rotation that bit is trying to produce. Boards less than 5" long have the greatest tendency to dip into the router bit opening, longer boards are easier.

- I've never tried this, but you could install a pair of zero clearance sub fences as described in the Wonder Fence manual, which can be found on either of our websites. Closing off the space between the bit and fence would dramatically reduce the boards ability to dip into the bit opening on through dovetails, and the sub fence immediately above the bit would completely eliminate this possibility on half blind dovetails. There's no need to have the right angle fixture hooked over the fence...it will track fine along the sub fence with some pressure inward/downward on the body (this is smart technique, regardless)

- Again, wax the snot out of both the table and fence, slicker is better. If you've seen our demos at woodworking shows, we keep our tables waxed up like a sheet of ice.

Let me know if I can clarify or address any questions - 888.804.6272 xt 4. Please e-mail me directly or call vs a PM through the forum...

Mark Mueller
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Taylor Design Group, Inc
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Carrollton, TX 75006

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post #10 of 10 (permalink) Old 04-07-2014, 08:33 AM Thread Starter
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Thanks for the tips Mark - straight from the mfr themselves! I'm attributing the first rounds of tear out mostly to my learning curve. I started out using a side board to hold the stock in place, but eventually went to the "hold left / push block top" method Mark speaks about above and had really good luck with the results. The idea of leaving the pins long and trimming them back is a great idea too.

Thanks again to everyone for the tips and helping a newcomer get better; my first set of drawers from rough stock to finished product had a few mistakes along the way, but I learned a ton and overall I'm pleased with how they turned out. It's certainly satisfying to see them and know that they're mine.
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