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Slot Mortising Feed Direction?
Posted: Tue Mar 31, 2015 8:40 am
by algale
If I am using the Mark V in drill press mode to cut slot mortises, is feed direction important? If so, what is the correct feed direction?
Edit: I may have found the official answer in PTWFE: "Position the workpiece against the left stop block so the bit will be at the first mark, extend the quill to penetrate the workpiece, and lock it. Then move the workpiece until it contacts the right stop block." In other words, left to right (or infeed to outfeed). Here's the photo indicating the correct feed direction (note the arrow on the stock indicating the user is pulling the stock toward the outfeed side):
I am still not sure why it matters when slot mortising. And if folks with experience in this operation care to chime in, I'd appreciate it.
Re: Slot Mortising Feed Direction?
Posted: Tue Mar 31, 2015 9:55 am
by BuckeyeDennis
The PTWFE process makes sense. As you feed the workpiece into the router bit, the cutting action of the bit tries to push the workpiece sideways, tangent to the cutting arc. In the setup illustrated above, if you follow their advice, that tangential force pushes the workpiece against the fence, which is nice and rigid. Do it the other way, and it pushes against the featherboard ... which may or may not have sufficient preload force to prevent the workpiece from moving sideways.
Re: Slot Mortising Feed Direction?
Posted: Tue Mar 31, 2015 10:42 am
by beeg
algale wrote:I am still not sure why it matters when slot mortising. And if folks with experience in this operation care to chime in, I'd appreciate it.
It's a matter of safety. If ya feed it from right to left. It's called a climb cut. Your feeding the piece into the bit with the rotation, which will want to pull the piece into the cutter making it hard to control. Feeding it from left to right your going against the bit rotation, which gives ya BETTER control of the piece.
Re: Slot Mortising Feed Direction?
Posted: Tue Mar 31, 2015 2:51 pm
by JPG
With 'slot mortising' the concept of climb cutting is unavoidable. As Buckeye stated the resultant force when feeding needs to be towards the rigid fence.
In the example, the edge between the fence and the bit is plow cutting, and the edge outside the bit is climb cutting. More important with slot cutting, is the area ahead of the cutter (end of slot). There the bit forces the workpiece towards the fence.
See 'correction/retraction' below!!!
Re: Slot Mortising Feed Direction?
Posted: Tue Mar 31, 2015 4:35 pm
by algale
JPG wrote:With 'slot mortising' the concept of climb cutting is unavoidable. As Buckeye stated the resultant force when feeding needs to be towards the rigid fence.
In the example, the edge between the fence and the bit is plow cutting, and the edge outside the bit is climb cutting. More important with slot cutting, is the area ahead of the cutter (end of slot). There the bit forces the workpiece towards the fence.
The areas in bold, above, were what I was thinking when I wrote the question, which made me think it would make no difference which direction you fed. But your last sentence makes a good point.
Re: Slot Mortising Feed Direction?
Posted: Tue Mar 31, 2015 6:02 pm
by jsburger
JPG wrote:With 'slot mortising' the concept of climb cutting is unavoidable. As Buckeye stated the resultant force when feeding needs to be towards the rigid fence.
In the example, the edge between the fence and the bit is plow cutting, and the edge outside the bit is climb cutting. More important with slot cutting, is the area ahead of the cutter (end of slot). There the bit forces the workpiece towards the fence.
Climb cutting can be very dangerous if you don't fully understand what you are doing. However in this case both sides of the bit are in contact with the wood so the the forces pretty much off set.
Re: Slot Mortising Feed Direction?
Posted: Tue Mar 31, 2015 8:53 pm
by charlese
JPG wrote:With 'slot mortising' the concept of climb cutting is unavoidable. As Buckeye stated the resultant force when feeding needs to be towards the rigid fence.
In the example, the edge between the fence and the bit is plow cutting, and the edge outside the bit is climb cutting. More important with slot cutting, is the area ahead of the cutter (end of slot). There the bit forces the workpiece towards the fence.
It is not too often we get a chance to correct this guy!
Well
This guy turns out to be me
No correction to the quoted words. Just repeat them.
Re: Slot Mortising Feed Direction?
Posted: Tue Mar 31, 2015 11:26 pm
by JPG
charlese wrote:JPG wrote:With 'slot mortising' the concept of climb cutting is unavoidable. As Buckeye stated the resultant force when feeding needs to be towards the rigid fence.
In the example, the edge between the fence and the bit is plow cutting, and the edge outside the bit is climb cutting. More important with slot cutting, is the area ahead of the cutter (end of slot). There the bit forces the workpiece towards the fence.
It is not too often we get a chance to correct this guy!
Actually the edge between the fence and the bit is climb cutting, and the edge outside the bit is plow cutting. No big deal but we want to get this straight.
More important is the area ahead of the cutter, as said in the quote.
Also the edge away from the fence is being pulled slightly toward the fence when the workpiece is moved from left to right as is the example. This force actually helps to keep the workpiece next to the fence, while the climb edge is having less force.
It is a good practice to use a small diameter bit for a shallow first pass. A shallow groove is followed by more passes to get to the desired depth. After the desired depth is reached, move the table backward a little, insert the bit into the slot (on the right side) and cut again. Repeat this until the correct width is reached.
Nay Chuck!
Draw it out.
The bit is rotating counter clockwise as viewed from the 'top'.
The workpiece is fed from left to right again as viewed from the top.
As far as climb/plow, the fence is irrelevant. The relative motion of the bit and workpiece determines which is occurring.
However one wants to use the fence so the forces are under better control.
When the workpiece is moved left to right, the rotation of the bit against the 'inside' work surface will resist the workpiece in the feed direction. That be plowing.
The rotation of the bit against the 'outer' work surface will pull the workpiece in the feed direction. That be climbing.
I
did however have the cutting action wrong. The bit will be cutting the 'trailing' end of the cut and thus will be pulling the workpiece AWAY from the fence.
Thus the fence provides a stop for the pressure required to keep the workpiece tight to the fence.
See 'correction/retraction' below!!!!
Re: Slot Mortising Feed Direction?
Posted: Wed Apr 01, 2015 6:37 am
by BuckeyeDennis
JPG wrote:
The bit is rotating counter clockwise as viewed from the 'top'.
Ya got yerself some of them rare left-hand router bits, and a headstock-reversing switch there, Red?
Re: Slot Mortising Feed Direction?
Posted: Wed Apr 01, 2015 10:58 am
by masonsailor2
One of the issues with slot amortizing is that you are cutting with both sides of the bit and it can grab or climb as you feed the piece. This can be dangerous but at the least give a bit of excitement. If you are mortising really hard material ( maple etc.) it can get difficult. One easy solution is to hog out the mortise first with a slightly smaller bit and then use the router bit for the final cut. Another hint is to cut the tenons first and cut them slightly larger than the mortising bit. 1/32 larger will do. Then after you have cut the initial mortise advance the fence and shave off in small increments until you get the fit you want. This is where the adjustable stop collars really shine.
Paul