Uneven Router Cuts

[cooterbrown]

Hey Guys,

Mounted the router to the BT3k and have it running.

Series of test passes with a roundover bit are giving mixed and inconsistent results.

It seems as though the cut is starting fine - but is petering out at the end of the cut. Like there was a 100% proper roundover cut at the beginning of the board and a 15% proper cut at the end of the cut (smaller area of cut).

I am using the BT3k Router accessory table.

This has been on the same board on every side - so that sort of takes the board out of the equation as being warped, bowed, or such.

I have two 30" sills I want to round over and wasn't thinking it would take all morning!

Any quick help as to what to look at I would appreciate.

[Brian G]

I'm sensing that the the trailing end is either lifting off the table, or pulling away from the bit.

Are you using a fence to help guide the stock? This might help you with keeping the stock against the bearing of the bit. Set the face of the fence so that the bearing is flush with the opening in the fence.

Are you using push blocks? They will help you safely keep the stock riding against the bearing.

[durango dude]

a) check that bit is tight in the collet (not all the way down, about 1/8" above bottom --- then tight)

b) Use starter pin ---- best way to introduce work to the bit.

c) If you're routing thin wood, use blocks/push pads
(you might - very sensibly - be pulling away from the bit)


My gut feeling is that your problem is the product of your body's natural instincts to avoid the router bit.

[mpc]

What are you using for a fence and/or how are you guiding the workpiece? And just where/how is the cut failing: as if the workpiece is pulling away from the bit or as if the bit is going downwards into the table/workpiece going up away from the bit?


I can think of one simple scenario that could lead to your situation:

If you are using a 2-piece fence, like the small pieces included in the Ryobi Router Accessory Kit, having the "outfeed" side fence not parallel to the infeed fence can make the workpiece rotate either into the bit or away from the bit. A crude diagram:
\._
the "_" is the infeed fence, the period represents where the bit is, and the slash is a horribly angled outfeed fence. Depending on where you apply pressure to the workpiece as it moves to the outfeed fence, you can see how the work will rotate clockwise moving the trailing end of the workpiece away from the bit. Angled the other way will result in the middle of the workpiece being pulled away from the bit until the very end of the workpiece clears the infeed fence, then that end will snap into the bit and get a chunk taken out of it.

Are you using a single fence with a "mouse hole" straddling the bit? That's a fairly common style router fence and is pretty foolproof. A simple 1x3 or 1x4 on edge, with a mouse-hole cutout around the bit, can be attached to the BT3's fence via T-bolts, the router accessory kit brackets, etc. Or just glue on another 1x3 to make an "L" shape (with a matching mouse hole) that you can clamp to your tabletop, the foot of the "L" faces away from the workpiece. Such a fence is pretty simple, quick, and most of all reliable. You don't have to align separate infeed and outfeed fences.

The edge of your workpiece board is straight, right? If it's not, it'll be virtually impossible to guide it along a straight fence for a consistent cut.

The other option is a bearing guided router bit in combination with a fence or by itself. A bearing guided bit, without a straight fence nearby, can cut oddball shaped workpieces. You'll need a "starting pin" in the table to act as a pivot/fulcrum to safely rotate the workpiece into the spinning bit to get started; once started you don't need to ride against the pin.

mpc

[LCHIEN]

there's two ways of using the roundover bit with bearing, one is with a fence and you bury the bit in the fence opening so that a straightedge across the front of the fence just kisses the router bit. The bearing should rotate but the strainght edge should not rock on the bearing, the straight edge should be in contact with the fence on either side of the bit opening. The other is to use the router bit out there bare naked, in which case you would be very wise to use a pivot pin.

Either way you can't overcut - the bearing prevents this. So for me, I always take a number of passes, you don't need to or even want to cut this all in one pass.

THe mechanics of routing are that too slow a feed rate and you will burn the wood. Too fast and it will chatter and slow the router RPMs down making a substandard cut. The solution is to make a fast pass feeding into the wood and taking off as much as you feel comfortable. Then make another pass, still fast so it doesn't burn. Each pass you push a little more and eventually you will see and feel the wood against the bearing. Make a couple of extra passes qucikly until you can barely hear a zzzzzz sound of the bit cutting wood. Remember you can't over cut because of the bearing.

If you're getting uneven cuts usually the bearing bit isn't getting all the way to the edge its supposed to follow, usually this means you need more passes. It could also be wood of varying thickness and/or dimples/uneven-ness in the edge. Or the wood is not flat.

[durango dude]

I was assuming the OP was using a bearing guide - which is pretty hard to mess up. The height of cut is fixed if you mounted the router correctly --- and the depth of cut is fixed by the bearing.

If you're using a fence - - yes - check fence alignment.

[Carpenter96]

It definately sounds like poor mechanics. You say every board is the same that it starts fine and then tapers off. If this true then it can not be the bit. It must be that you are not holding the wood down on the table or you are not keeping the wood againist the bearing. Practice makes perfect and we all need to practice. Keep tring you will get it.

Regards Bob