B-52 Tail shaped Walnut cutting board


difalkner

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  • 2 weeks later...

From the videos you've put up, it looks to be a very stable machine. I don't hear any chatter or motor whine at all. For the most part, I've had most success in solid woods using either a compression spiral or a very slight upshear bit, so long as your parts are secure. Definitely a compression cutter for plywood and MDF. 

I noticed in your video that you looked to be moving along at a good clip in shallow (1/4"?) passes. Good practice vs cutting slower and deeper. You get better chip evacuation and longer tool life, and most likely a better cut quality. 

I don't know if you're familiar with Darrell Peart. He's a Greene & Greene style furniture maker in Seattle. He's been on a learning curve with his CNC for a couple of years now. He posted a good link to the CNC blog for Popular Woodworking about tool selection and use that you might find useful. Feeds, speeds and tooling are the hardest part of the CNC learning curve, in my experience.

Keep the great videos coming!

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My typical speed/feed with 1/4" upcut bit is 18,000 rpm at 100 ipm although I often do small tight cuts at 75 ipm just because it seems like violent movement in such a tight spot.  On longer straight cuts without tight bends I increase it to 125 or 150 ipm.  On the Walnut pieces my depth of cut is usually 0.09375" and I know I could go deeper but I like getting clean cuts straight off the machine and I don't have to be concerned about tearing fibers.  I don't have any compression bits but will definitely try some soon.

There's some great stuff on Darrell's site, Mick.  I've added this to my reading list, growing longer every day it seems.  Thanks for the reference!

Glad you like the videos - the next one will be on the building of a downdraft sanding box; not real exciting but I'll post it anyway.

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David, not knowing the specifics of that machine, I can't say for certain, but it's typical that in the small, tight spaces the machine would not fully accelerate up to a (fast) programmed speed anyway. For example if I'm doing inlays in a 3/8" x 1" letter and program it to 200 ipm, the machine would most likely not hit more than about 60 or 70 ipm anyway. Likewise most software has built in acceleration and deceleration parameters that compensate for tight radii and corners, slowing the machine so it doesn't overcut or burn.

I had a chance to read through all the posts so far on the  CNC blog for Popular Woodworking and the tooling info is very good. I had one minor issue with his comment that single flute bits are no good for woodworking. There are single flute compression cutters designed to work well at relatively low feedrates in MDF and plywood. One (unsolicited) piece of advice I might throw out there - when I teach the tooling portion of CNC use I recommend that people program at a considerably faster feedrate than they will probably use. The limiting factors should be the machine's capability, the ability to secure the part to the table and the cut quality. The goal is to find the point that one of those factors fails - the tool snaps, the part moves, the cut is poor - then back off about 10 - 15%. The reason for this is that the tooling will last longer and stay sharper at higher feedrates due to better chip ejection. Slow feedrates often lead to chip buildup, ergo burning.

Can't wait to see what video you post next!

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Those are good points, Mick.  My rapids are typically 600 ipm and I have Mach4 configured with the motors at 750 max.  Nate told me when I bought the frame that 1800 ipm isn't out of the question for this machine but he recommended not going over 1200 ipm.  After seeing 600 ipm I'm not sure I want to see 750!!

I have acceleration set to 75 and that seems to work ok.  I toyed with slowing that down and at one point I had it at 100 but that seemed to jerk the machine around and you lose that nanosecond of response time if you have to hit the E-stop quickly.

From what I've seen of this machine the limiting factors are far enough out that I don't expect to hit them often.  It would be a good educational move for me to put some less expensive wood on and see what cutting at 250 ipm looks like.  It seems from the minute I fired it up there were jobs for other people and these were on Walnut and Mahogany so I don't want to waste any of that.

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