Drill MOP Spiral Depth Increment on MDO plywood

[airnocker]

Got the zip file, thanks.

Ok, good to know that using a short flute length on a long enough shank for full cut depth hasn't been an issue for you with wood.  I'll give it a whirl on my next drill and pocket MOPs in 3/4" MDO plywood.

That's neat how your other dust aspirator has sides that can flip up out of the way when needed.

[dh42]

Yes, and it's a stroke of luck that the "door" remains in the open position LOL .. it's because my piano hinge is fixed on a not very flat surface, so it gets stuck !!! 

++
David

[airnocker]

Ok, another great secret of the trade from David on how to create a hinged door flap that has position brakes. 

This uneven surface method is worth noting.  Sometimes the best discoveries are complete accidents.

[dh42]

Sometimes the best discoveries are complete accidents.

+1

[Bubba]

Here are the pictures I promised showing the vacuum shout on my router . The spindle is Milwaukee router motor with air exhaust on (bottom) router bit side. The shoe allows for about 90% of the air to exit on side instead of the bottom. The shoe plate is 0.25"thick aluminum with pocket machined 0.220" deep. Very pleased with its performance, Its allows for very short toolbits to be used, and nearly '0' chips escape 
The 1/4 inch dia router bit seen in the picture is sticking little bit because just finished routing 1.5 inch thick board '

Hope this helps

[Bubba]

Because of file size limit, here are additional pictures.

[airnocker]

Thanks for sharing, Bubba.  Very nice, detailed photos.

[jimmer]

I did a profile MOP test cut based on Bubba's parameters and it did the first outside profile roughing cut (.5" DOC @ 45ipm and 20000 rpm) and although it was loud it worked okay, so I continued with the outside profile finishing cut using .375" DOC @ 60 ipm and 22000 rpm.  It too seemed to work okay at first glance but had minor issues. The 2nd depth cut was slightly wider (.03125") around the perimeter of the cut than the 1st DOC.

I then did an inside profile roughing cut (.5" DOC @ 45ipm and 20000 rpm) and the mill path went in the opposite directions than the first one.  About 3/4 around the profile shape the bit broke where the flutes meet the shank of the bit, so my machine and bits are not robust enough for these aggressive parameters.

Photo attached:

How was the workpiece was being held ? I can't work it out from the photo.

[airnocker]

Hold-downs are 4 counter-sunk 2" wood screws offset about 3/4" from the corners.

[jimmer]

Like this? 

That looks ridiculously flexible to me so I'm not surprised that the piece got dragged sideways by the cutting forces.

I see from the previous pictures and video that this is your usual clamp method (external perimeter clamp or corner screws, with stock only just bigger than the piece).  Are you using something sticky under the workpiece as well? 

I'm surprised you don't have more accuracy problems, even with delicate DOC and speeds.  I'm no expert on clamping because I mostly use vacuum hold down, but when I do clamp I am very wary of flexing. Where possible I put screws through the workpiece.

If you are going to experiment with more aggressive cuts try using larger borders on your stock. Even better use tabs to retain the stiffness in the stock.

Another tactic would be to use aggressive cuts followed by a shallow cut at full depth, eg 3 cuts of 0.0.22" followed by 0.10" ,  take all the parts down to eg 90% depth before cutting any of them free. 



I've only just started using 18mm birch plywood.  One tactic I've used for a clean cut is to score all the cuts using 1mm doc with my 1/8" downcut bit, and then do the serious removal using my regular 1/4" upcut with 3x doc 6mm.  I'm sure 2x 9mm doc would work too.

[airnocker]

Like this? 

That looks ridiculously flexible to me so I'm not surprised that the piece got dragged sideways by the cutting forces.

I see from the previous pictures and video that this is your usual clamp method (external perimeter clamp or corner screws, with stock only just bigger than the piece).  Are you using something sticky under the workpiece as well? 

I'm surprised you don't have more accuracy problems, even with delicate DOC and speeds.  I'm no expert on clamping because I mostly use vacuum hold down, but when I do clamp I am very wary of flexing. Where possible I put screws through the workpiece.

If you are going to experiment with more aggressive cuts try using larger borders on your stock. Even better use tabs to retain the stiffness in the stock.

Another tactic would be to use aggressive cuts followed by a shallow cut at full depth, eg 3 cuts of 0.0.22" followed by 0.10" ,  take all the parts down to eg 90% depth before cutting any of them free. 



I've only just started using 18mm birch plywood.  One tactic I've used for a clean cut is to score all the cuts using 1mm doc with my 1/8" downcut bit, and then do the serious removal using my regular 1/4" upcut with 3x doc 6mm.  I'm sure 2x 9mm doc would work too.

My bad, I thought you were referring to the video I posted a few days ago.

That piece had two screws which are evident in the photo.  The lower piece was the one cut out with holding tabs securing it in place on both the profile cuts.  Granted, the automatic 1/8" holding tabs were not sufficient when doing the inner profile cut which no doubt resulted in vibrations.  This was a piece of scrap to test Bubba's DOC and feedrate, nothing more.

My past practice over the past decade has been far more conservative.

[jimmer]

OK so you use tabs, that's good    

I didn't (still can't) see any evidence of them in the photo, maybe that's because of how you remove them?   How many tabs were there on each of the profiles?   

[airnocker]

OK so you use tabs, that's good    

I didn't (still can't) see any evidence of them in the photo, maybe that's because of how you remove them?   How many tabs were there on each of the profiles?

All total there were 24 tabs, 12 on outside oval profile, the first profile to be successfully milled, and 12 on the inside oval profile the one that was 3/4" complete when the bit broke.  After the piece was unscrewed from the table, I cut thru both ends of the tabs with a fine miter hand saw to free up all three pieces.

The purpose for my wanting to cut the thin-walled oval was to test how much and what degree bit vibration occurred which would have manifested itself with the walls of the cut not having undulations.

My .015", .025, .05 and .125" DOCs at 20-45 IPM, 10000-13000 rpm in this 3/4" MDO plywood for other part milled produced beautiful, straight and smooth wall profile cuts.  So this was just a test to see how much speed I could get in cutting.   

[jimmer]

1/4" DOC seems pretty good with 1/8" cutter.  That's more aggressive than I would think of using, maybe because I mostly work in plastic and use DOC = 1.0D       

I guess my point if I wanted to drag it out longer is that your tests were not like-for-like. Even with the tabs, there is more flexibility in the restraint than with the first profile.

check this out (1/8" cutter 3/4" DOC):  https://www.youtube.com/watch?v=n-1w5Yg0AJ0

[airnocker]

Thanks jimmer, the compression cut end mills are great for getting aggressive DOCs in wood.  I had read up on them a few weeks ago (don't have any myself for now).