3/8" 3-flute downcut - Shapeoko Pro XXL (+HDZ)

How To Machining
1

Context:
I have a surfacing process which I am trying to reduce the time of.

Currently, at 18k rpm, I’m using a 2-flute 1/4" downcut endmill to do a:
(1) Roughing pass - 0.3mm-0.5mm DoC; 3000mm/min feed; 90% stepover,
(2) Finishing pass - 0.1mm DoC; 6900mm/min feed; 10% stepover.

However, this process, over the number of units I have, takes 2 hours minimum to complete surfacing a batch and I think i’ve tapped out how far I can push the feedrate and play with the stepover %'s for this bit. I aim to cut this time as much as possible.

I have a makita palm router on my Shapeoko and found/bought an official 3/8" collet supplied by makita which is compatible with the specific palm router model used on the machine. I have now bought a 3/8" 3-flute downcut so I can switch out the 1/4" for this to cut the procedure time for this step by between a third to a half.

I have no intention to use this bit for anything other than to surface these inlays at an absolute maximum of 0.3mm-0.5mm DoC. Because its such a shallow maximum DoC and a downcut version of the endmill, I figure I have enough tolerance to accommodate this size of bit (3/8" 3-flute DOWNcut) without coming close to exceeding the rigidity limit of the Shapeoko Pro XXL (with HDZ)

Question:
Does anyone have any advice before I give this 3/8" downcut a crack? Perhaps I reduce the rpm’s from my standard ~18k to like ~12k coz it’s got some weight to it? Any input from people with experience would be greatly appreciated

2

I have the S5Pro, 65mm spindle and ER-11 collet. I purchased an 8mm and 5/16th collets for it and I use the same feed/speeds as I was with the 1/4” bits. Most of these feed/speeds are default from CC to start with and then I adjust as needed and usually are both increased a good amount.

Not sure if that helps you or not. Lots of folks on here with your setup though.

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While the defaults are a good starting point, as one increases the tooling size, one will drift away from their working envelope.

Best to understand underlying principles and work from them:

and also see the various videos at:

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4

What about a 1" or 1-1/4" surfacing bit? With such little material removal, if you’ve got the Z-axis near-perfectly trammed, a wide surfacing bit may work. What’s the stock material?

5

Yeah, I had considered that but the shapeoko pro bit setter is very narrow diameter (unlike the improved one on the shapeoko 5), so the surfacing bits will always not hit the probe properly at the correct depth where the blade actually is. Therefore, I gotta focus on straight bits. Ergo, the 3/8”

The stock is maple and walnut

6

Whenever I use my large diameter surfacing bit, I just stick a large washer atop the Bitsetter to contact the bit properly. As long as you keep the washer/spacer on the Bitsetter from the first measurement taken since powered on & for subsequent checks, it works fine.

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I found a left-over piece of Al bar stock (1/8" thick, 1" wide), and cut a 1" square from it. I glued that to the top of my BitSetter, and now I can use wide bits no problem.

The actual height of the BitSetter doesn’t matter, so long as it is consistent from measurement to measurement.

8

I had the same problem with my surfacing bit. I moved my bitsetter slightly so the ‘wings’ of the surfacing bit hit, yet straight bits still hit properly - just slightly off-center.