What is the right - best bit ?????

[woodshop]

cribbage-Rio.jpg

It's difficult to make something like this too fast.
We prefer to cut slower than the big production shops.

[Rtalexand]

This is a terrific thread. Great info. I recently attended the Cabinet Class at ShopBot for the Cabinet Parts Pro software. I had been using 1/4" bits for all my cabinet work. I am semi- retired and have had my ShopBot for a couple of years and am just a hobbyist, but enjoy building cabinets for myself and friends. In the class, Ryan was using a 3/8" mortise compression from Onsrud (60-123 MW) to cut cabinet parts from 3/4" MDF in a single pass on the PRS Alpha. I am now using the Onsrud 60-120 MW (single flute for my PRS Standard) and I cut a single pass on 3/4" Maple plywood. Using the chip load calculator and listening to the bit work, I am running 288 IPM @ 15,000 RPM. I get a great cut that I can take straight to the edge bander. I can cut a full sheet of panels with dadoes and rabbets in under 40 minutes. So far I have cut over 6 sheets using these settings with no degradation in the edge quality. The bit is slightly warm to the touch when it is done with a sheet.

I hope you don't mind a hobby user jumping in, but the cabinet class was very enlightening ... Thanks

[woodshop]

Amana Tool® Item #46171

Just ordered 2 of the above compression bits.
We shall try these out, compare the cuts, maybe throw some pictures up as proof.

But will probably stick to my standard 60 ipm.

[Martin Reid]

We like that LAST PASS REVERSE DIRECTION option. Finally figured out to put a value in the ALLOWANCE field to get it to work.
Nice clean cuts!

(Thanks John and Dave for the confidence to push our machine to the limits. I guess I'm trying to get a hundred miles out of one bit, ha.)

Dear Dave

Things have moved on from conventional vs climb; so I feel I could contribute another two penn'oth.

From the days of being an apprentice carpenter using a hand router was always 'slow and steady gets the best results'. Moving away from this stand point has proved to be quite difficult and whenever things go astray it is always the fall back position.

But when not using a hand fed machine other issues become apparent.

(1) Taking small amounts off each pass is only working the 'tip' of the cutter.
(granted the reverse last pass elevates some of this by using the whole cutter for the last pass)
A good stating point is a pass depth about equal to ½ the cutter diameter, with the aim of working towards a pass depth equal to the cutter diameter.

(2) Incorrect feeds and speeds increased the temperature of the cutter and reduce the life.
(Generally in plywood - you should see 'shavings' or 'chips' if you are creating 'dust' you need to reduce the RPM or increate the Feed Speed (or a combination of both).

PLYWOOD

The problem with ‘machining’ plywood is the glue lines. On WBP plywood this resorcinol formaldehyde glue is very strong and durable but is also very hard and can dull the cutters. A strategy to vary the depth of each pass to ensure that different areas of the cutting edge cut against the glue line will increase the life of the cutter.

RouterCutter on Plywood.jpg

'trying to get a hundred miles out of one bit'

This is the aim of most especially those that are paying for their own cutters.

So for all the issues taken above if I can increase the depth of each pass and thus reduce the number of passes for each part. In your case to go from 5 passes to 4 should give you 25% more parts per cutter.

Sincerely and in good faith
Martin

[jTr]

In the class, Ryan was using a 3/8" mortise compression from Onsrud (60-123 MW) to cut cabinet parts from 3/4" MDF in a single pass on the PRS Alpha.

I would dearly love to see that - I mistakenly ran a 1/4" bit in one pass through MDF and the result was a horribly jagged cut, like I was attempting to cut a straight line with a jig saw. Turns out my pinion gears were worn, but still - I'm simultaneously freaked out yet intrigued about trying this. Just not confident I've got the finesse to tighten up my machine to handle this aggressive cut. (2012 PRSAlpha 9660 2.2HP spindle)

Do you recall feeds/speeds? I'd love to remove 1/4" bit from cabinet cutting routine - 5mm for hardware holes and pins, 3/8" for dados / rabbets. If I could leave the 3/8" in place for cutouts, it would be nice...

Jeff

[dlcw]

A good compression bit will last about 25 sheets (of plywood, 18 particle board) if your RPM and feed rates are correct. The thing to listen for is a bit that is screaming. A screaming bit is a hungry bit. You need to feed it faster or slow down the RPM. I cut 3/4" maple plywood (Armorcore) at 300ipm in two climb passes and one conventional pass.

For mortises in the plywood I use a 1/4" down spiral bit at 300ipm 14K RPM. When I cut plywood, I don't hear the cutting operation nearly as much as the vacuum hold down motors. If I hear the cutting operation (screaming bit), I know I have to increase the feed rate (preferred action) or decrease the RPM's. I've been considering pushing it to 360ipm because I still get a little chirping (other than corners) when cutting. 60ipm is wasting a bit and causing it to prematurely dull.

To give you an idea of feed rates. When you get done cutting all the parts on a sheet of plywood, the bit should be little more than room temperature when done. If it's hotter than that you are dulling and shortening the life of the bit - A LOT!!. Just make sure the bit is not spinning when you touch it. LOL.....

One other side note, when cutting with a compression bit, make sure you plunge into the workpiece the depth of the upcut part of the cutter before beginning you ramp. The up cutters will splinter the edge of the veneer of the plywood if you don't do this. In VCarve or Aspire, you do this by setting your start cutting depth just a hair deeper than the upcut part of the bit. Than do your ramp to cutting depth. Those upcut flutes are VERY efficient!

[woodshop]

Thanks, Martin. I get it. Thanks.
Yes, finally someone understands the hard glue in plywood thing. That's why I choose to go slow.
Also, one must think of those clamps holding down your piece. Pushing too fast and too much of a bite can give your clamps some stress.

IMHO, we can debate the SLOW vs FAST thing all day.

[steve_g]

Dave…

Now that I see your product, I’m not sure a compression bit is the right one for the job! What I’m seeing are numerous shallow pockets, almost certainly shallower than the up-cut portion of a compression bit.

I’ve never cut stair stepped pockets like this in plywood, so my next comments are just gut feel!

If this were my job here’s how I’d approach it:

First, I’d cut the blank perimeters with a compression bit.
Second, I’d set up 2 or more locating jigs that hold the parts with cams. I’d use multiple jig locations so I can reload one station while the Bot is cutting on another. With a little editing, you can have the program continuously go from station to station … or pause at a neutral location waiting for a keystroke to continue.
Third, I’d cut the peg holes… Cutting the peg holes before the pockets lets the pocket pass shave the tops of the holes that likely have splinters pulled up. Hopefully the peg holes are a bit larger than the bit you use for this process… that way you can spiral cut them without retractions for chip clearance.
Last, cut the contour pockets with a down-cut spiral bit.
Oops, looks like there’s some v carving in there also. Do it any time that works!

I often go to great lengths to minimize or eliminate bit changes but there’s no way to do it on this project, that’s why I cut the blanks first, so the bit changes are done for batches.
I’m curious as to how others might approach this job… let’s hear from ya’all!

SG

[Rtalexand]

The class used the Onsrud Chip Load Chart. For MDF, the Chip Load is .019-.021. As I recall, max speed for the Alpha is 600 IPM. So, using the calculator; setting CL=.02; Speed=600; 2 Flutes; the spindle speed is calculated @ 15,000 RPM. Ryan suggested using the maximum router speed to obtain as much horsepower as possible. Slower speed, less horsepower. For my PRS Standard, I had to drop to a single flute bit since max speed is 300 IPM. Once I used these settings, I started getting really nice chips from the cuts.

Yes, it's really nice to combine the toolpaths for the 3/8" bit to do the straight and blind dadoes on the 3/4" plywood and MDF with the profile cut in one file.

If anyone is interested, my Shopbot (used) came with an Onsrud 60-123 MW 2 flute mortise compression bit that I can't use.

Regards, Rick

[woodshop]

The cribbage board was just an example of some of the things we make here.
The subject of my original questions were all about maple plywood and editing passes.
Thanks