Router Problem

[steve-norrell]

A not-so-funny thing is happening at the router table.

Using "The Setup" shown in the picture the depth of the dado changes while I am cutting it. It deepens considerably, then returns to its original depth. The result is shown in "The Problem". The dust collection system was on. The bit is a 3/16 straight bit, set to cut a 3/16 deep dado.

I double checked the router bit and made sure it was tight in the chuck, I have not experienced this problem when I do not use the 'long featherboard'

I suspect that the 'long featherboard' blocks air flow and the additional heat generated causes the bit to rise, thus deepening the dado.

Anyone experience this problem? How do I solve it?

Thanks, Steve

[Thom2]

If you're using a plunge router under the table, are you sure the plunge lock is functioning correctly??? ... Off the top of my head, that's about the only thing I can think of that would allow the bit to move and then return to it's previous position.

If the bit were loose in the collet, the bit should rise and stay risen (risen? rose? rosed? *shrug*)

[crokett]

Does your router have dust collection under the table as well as in the fence? In that setup the above the table dust collection is not doing much sincethe wood is blocking any dust being pulled from the top.

If a plunge router, check plunge lock as Thom suggested. What is the router plate made of? I had one made of clear poly that would flex under load. Is the wood bowed? If it is not perfectly flat on the table you will get this result. I can't see the bit rising that much due to heat. From the pic it looks like the depth difference is almost 1/4". That means the bit would be getting 1/4" longer.

[Tequila]

Is it the correct depth at the beginning and end, or at the middle? If it's too shallow at the ends, chances are that the workpiece just lifted up at the beginning and end. Maybe your plate's not flat, or maybe the workpiece just never seated all the way.

A featherboard on the rail to hold the piece down could help. You also might want to try taking a shallower pass and see if you get the same results.

[LarryG]

Deeper at the ends usually means a sagging plate. Deeper in the middle ... now that's just weird.

Have you checked for end play in the router's armature? (Although if the bearings were THAT shot, you'd surely be hearing some noise ...)

[John Hunter]

I would also be checking the router collet and the bit. I had this happen with a spiral bit I bought at the Wood Show. Found the shaft was just a bit undersized and even though the collet was tight it allowed the bit to climb.

[steve-norrell]

I should have mentioned . . .

The router is a Bosch motor mounted in a JessEm Lift; no base. The bit is 1/4" shank. The difference in depth is way more than can be explained by sagging plates -- its at least double the desired depth of 3/16". Dust collection is done both under the table and through the fence. I forgot to show that I did use feather boards on the fence.

Since the router is mounted under the table, the plunge router answer can't apply because a loose plunger would make the router moved DOWN. Also, since it is making a deeper cut, the bit would have to move UP relative to the wood; the wood can not move away from the table (if it did I would get a shallower cut).

I blow out the collet every time I change bits. And, I did tighten the collet as much as I could.

I have not measured the diameter of the bit shaft, but that might be part of the problem. The bit is a Bosch bit, purchased at the Borg.

This does not (and has not) happen with any other setup.

Thanks to Larry, Joe, John, Dave, and Thom. Maybe this is one of those weird things that started occurring when "Murphy's Law" was put on the books.

Thanks for the help. Looking for more advice! Regards, Steve

[LCHIEN]

You don't say how much the shift is but it looks like maybe more than 1/8" Maybe 1/4"?

Sounds like you are sure that the wood is not lifting off the table?

Then What I would do is this: Make sure the router is unplugged. Now grab everything associated with the router and bit and wiggle it up or down to see that it is solidly locked in place (and the bit height doesn't change relative to the table top):

• Push on the edges of the router table
• pull and push on the router motor body
• push and pull on the router bit (careful don't cut your hand)
• push and pull on the mounting plate
• push and pull on the router base
• push and pull on the insert, the fence, the handles, the cord etc.

If anything moves the bit, then there's your culprit.
What's unusual about your problem is that it (the bit) apparently goes up and then down again. Most things that slip (not locked down properly) just go one way. The things that goes both ways usually are related to motion of the wood. With a long skinny piece like that, you would bear down with the most vertical hold down pressure when the center was over the bit.

[LarryG]

I suspect that the 'long featherboard' blocks air flow and the additional heat generated causes the bit to rise, thus deepening the dado.

Based on the additional info you provided, my best idea at this point is a variation of this: something is haywire with your router lift and it's allowing the router to move up and down at the middle of the cut, when the DC is presumably pulling hardest on the workpiece.

One thing I'm unclear on: can you repeat these undesirable results? You said nothing like this happens with any other setup, but has it happened more than once with this setup?

[Thom2]

Since the router is mounted under the table, the plunge router answer can't apply because a loose plunger would make the router moved DOWN. Also, since it is making a deeper cut, the bit would have to move UP relative to the wood; the wood can not move away from the table (if it did I would get a shallower cut).

I know we've resolved that this is not your problem, but just to clarify, with something like the Hitachi M12V under the table (and using the microadjuster), the microadjust will keep the motor from moving down when the plunge lock is disengaged. Also, some bits have a tendency to pull themselves into the stock. With a disengaged plunge lock, they would pull the motor assembly up while you were feeding your cut, then the instant you stopped to switch feed hands (or whatever) this could allow the motor to fall back down to it's original position.

While your router setup blows my theory, you may be able to pick up something from the explanation that may point you in the right direction to finding the culprit. I know that I myself would SURELY want to know why this was happening because it sounds to me like a serious safety issue. (think about that bit poppin' thru the top of the stock while your feeding).

[steve-norrell]

One thing I'm unclear on: can you repeat these undesirable results? You said nothing like this happens with any other setup, but has it happened more than once with this setup?

Yes it has happened more than once. I made all the usual checks after the first time, put everything back together, tried again. It did it again. I did not try a third time. It did not and does not happen with any other setup that I have used. The bit seems to move up and down with no sign of side-to-side movement.

I have not yet measured the diameter of the bit shank. I will do that and try LCHIEN'S ideas later today.

Thanks again. Regards, Steve

[steve-norrell]

Update but no answers . . .

I checked out the suggestions by LCHIEN and no loose items could be found. The diameter of the bit shank was exactly 0.250 in (see John Hunter's comment). So, to paraphrase good old Sherlock, when you have eliminated all other causes, you must accept the obvious. I probably overlooked something that caused the bit to rise, then lower while cutting the dado.

I did cut the dados as planned by using BenchDog featherboards instead of the long featherboard. Everything worked fine and the product is shown in the photo.

These are sample boxes for a grandson's rock collection. The problem dados hold the oak plywood pieces in the lids. The lids are designed to align the two boxes when stacked. The top box is sitting on the lid of the lower box. The corners of the boxes are lock miters.

Thanks for all of your advice. Regards, Steve.

[cgallery]

Update but no answers . . .

I'm afraid that isn't gonna do. Please continue making rock boxes until you discover the problem. Then, let is know.

Those are some mighty nice looking boxes, BTW.

[Wood_workur]

could it tear out? is your collet also .25?

[leehljp]

What is your router top base made out of? The white part? (Not the feather board but the part under it.) Could it be flexing any? I can see your T channel, but what kind of channel or attachment is under the featherboard? To me, it looks like the FB apparently has an attachment point under it rather than in the visible T track.

If so, this might suggest some weakness (two or three T-Track slots) that under some cirumstances that allow for the whole top to flex. Remember that something can be real strong and very ridgid, but under the right vibration or harmonic will begin to flex.

Since it looks like you might have more built in attachement points than is visible because of the feather board, the harmonics might be affecting this.

This is a 1 in a million shot but when all else is excluded, time to start looking for the long shot answers.