Help with cutting circle frames

How To
1

Hi Everyone,
I’m trying to make a bunch of circular picture frames, and am having trouble. It’s an incredibly simple cutting program, and I’ve done it with success several times, using cherry, as well as maple, only now I can’t seem to get it to work.

I start with an 8" square of hardwood, 1" thick. It is comprised of two pieces of 1/2" thick wood, laminated cross grain to each other for strength. Then three pockets are cut, followed by concentric slots, going from outside in. I’m using tape to hold down the wood (for now), and leaving a .2mm skin along the bottom.

I have done this program about 6 or 7 times without issue. But on the latest work piece it’s having problems. The spindle is getting stuck, dropping steps, and making a kind of “bottoming out” noise when it gets to the last few passes of the slots. It does not seem to happen on the pockets, nor on the cuts adjacent to the pockets.

This made me think it was due to chip clearing, but it seems odd that it would start happening now, after being run perfectly well so many times before.

I tried modifying the g-code to reduce the speed and the plunge significantly, but it doesn’t seem to have made any difference. I have no idea why this is suddenly misbehaving! Could it be a problem with the machine?

Here’s a few photos, in case they help:

2016-11-17 11.46.02.jpg3024×4032 2.12 MB

2016-11-17 11.46.13.jpg3024×4032 2.04 MB

And here’s my files:
concentric wood master 25.1mm.c2d (11.9 KB)

concen wood 25.1mm stock.nc (1.1 MB)

concen wood 25.1mm stock.egc (1.5 MB)

2

@MrHume

Wood will move, and if your deep in a pocket, the un-fluted section of your tool could be rubbing- creating friction.

Wood will also vary from board section-to section so ultimately you may need a longer LOC tool.

Or if you can open the gap up so your not in side to side contact as well as full depth.

1 Like
3

I’m not really sure what the error is. Could you make a short video and post a YouTube link to it so that we better understand the problem?

Couple of questions:

  1. What machine?
  2. Have you changed the cutter? If yes, what is the LOC?
4

Hi @ApolloCrowe, thanks for the super fast response! I thought it might be something to do with the depth of the slot, but I don’t understand why it’s just now starting to occur. I have actually cut versions of this that were even deeper - here’s a photo of a finished one on top of the ruined one. (don’t you just love the difference between finished and rough wood?)

2016-11-17 12.51.55.jpg4032×3024 2.12 MB

I had some problems with my wiring harness to the z-motor, which I fixed by resoldering the wire into the little white plug, and then coating the thing in hotglue for reinforcement. Do you think it’s possible this is related? It seems rather dubious, but I wonder if the spindle isn’t losing a little bit of power somewhere along the line? Or maybe the spindle drive belt is too tight? It was loose, so I tightened it, but not by much…clearly I’m grasping at straws here!

I have to cut a lot of these out, and would rather cut them as quickly as possible, so enlarging the slots is not my preferred option. Any thoughts? Could it be my cutter is dull? How do you tell if it is? It feels sharp to me, but I’m not too sure how to check.

5

Hi @RichCournoyer, thanks for getting back so quickly!

I’m on a Nomad 883 classic.
I don’t have a video, but I’m going to run another job and see if the same problem occurs, if it does I’ll video it and post. I will also try changing the cutter. I know this is a total newb question, but how do you tell if your cutter is sharp?

6

@MrHume

Try a new Cutter to start.

The Z stepper and the spindle are not related power wise.

Enlarging the slots would alleviate the full depth situation that I think is happening.

Again- wood will expand and move as you remove material, and every peice of wood is different.

7

Lets see the tool, and I would love to see more of these parts, Really nice.

8

I use a 10X eye loop and look at the cutting edges. (ebay $4)

Look at a new one cutter, now look at a used one and look for

  1. chipped edges,
  2. worn cutting edges,
  3. wood resin stuck to the cutter, etc.

Some guys will see how it feels against their fingernail (old vs new), scrapping the nail lightly.

I know this may not be a popular answer since Carbide3D only sells end mills (originally designed for cutting metal), but I recommend using QUALITY Router cutting bits from a place like Rockler, etc.for cutting wood They are designed for cutting wood, and produce a better surface finish in my opinion.

2 Likes
9

Please use the operating checklist — http://docs.carbide3d.com/article/41-machine-operating-checklist — I suspect your endmill has become dulled, or it may be that a belt is loose or wearing.

Another possible consideration is moisture content, and the wood in question may be “reaction” wood, which wants to bend / straighten after being cut, or it just may be tougher, harder grain.

Best long-endmill which I’ve found is Garr Tools extra reach tools: Shapeoko CNC Router, Rigid, Accurate, Reliable, and Affordable

excellent quality, long narrow bit w/ a long cutting length which makes workholding and fixturing much easier, and making through cuts (w/ a suitable number of passes) on 1" material feasible.

http://www.garrtool.com/tooldetaillogin.jsp?edp=41030

10

Here’s a couple photos. It was surprisingly hard to get the camera to focus on the end mill, so hopefully these are clear enough.

PB170339.JPG2572×1715 2.69 MB

PB170337.JPG2572×1715 2.21 MB

I will definitely post more about these frames very soon, they are made largely on the Nomad, and then hand finished, and they’re coming out great!

On the subject of wood, assuming I get a cutter in there that is properly sharp, of course, how much should I expect to have to vary my feeds and speeds between Walnut, Cherry, and Maple?

Thanks, @WillAdams and @RichCournoyer, I have ordered some new cutters from C3D, and am also going to look into other brands.

11

@MrHume
Heres some pics from great wood book.

Looks like Walnut is the hardest of the 3 species you mentioned, Of course, there are lots of different species of Walnut, and Cherry and Maple.

Check the specific gravity number of the wood for its density.

FYI: A wood with a specific Gravity of 1 will not float, example: Lignum Vitae (IMO: the king of all woods)

Screenshot 2016-11-17 13.14.42.png1144×806 1.15 MB
Screenshot 2016-11-17 13.14.26.png1137×865 1.17 MB

Screenshot 2016-11-17 13.15.48.png951×898 1.17 MB

Screenshot 2016-11-17 13.15.12.png1112×874 1.13 MB

1 Like
12

Thanks for showing us this book @ApolloCrowe!. I’ll be buying one. Eager to learn about woods.

13

I wonder if using a 3-fluted cutter might help, since the cutting flutes won’t be directly across from each other in the slot?

Randy

1 Like
14

Some potentially useful references are listed at: http://www.shapeoko.com/wiki/index.php/Books#Wood

esp. note http://www.fpl.fs.fed.us/documnts/fplgtr/fpl_gtr190.pdf Wood Handbook: Wood as an Engineering Material

15

That’s an interesting idea. Is the Nomad powerful enough to use 3 fluted cutters? I think I have one I ordered by mistake and then thought I couldn’t use…

16

Ok, so here it goes. Worked very well right until the final pass, at the end of which it gets stuck, drops a couple steps, and generally ruins my day.

Put my sharpest cutter in there, so I think that let it get farther. Wish I knew why this was happening now, after doing loads of these with no trouble. I need to get them done, soon, so I’m starting to get a bit worried!

If I have no choice but to enlarge the slot, how would I do that? I made these models in CC. Would I just have to add another circle and tell it to do a pocket cut? Or what?

Do you guys think using a 3 fluted cutter is worth a try? I happen to have this one, from Harvey Tool:
Cutter Diameter: .125" (1/8)
Length Of Cut: 1.000"
Overall Reach: 1.000"
Flutes: 3
Shank Diameter: 1/8"
Coating: AlTiN
http://www.harveytool.com/ToolTechInfo.aspx?ToolNumber=33708-C3

17

It looks like your feed rate is way too high for a Normad.

1 Like
18

I got that speed using G-Wizard, and have been able to run at it pretty well up till now. I did think it was too fast when I first started experimenting with it, but after a few nervous attempts with no issues, it seemed like it would be ok.

I also tried lowering the speed and the plunge rate by nearly half, but got the same result. Admittedly that was with a dull cutter…

19

@ApolloCrowe If I do need to make the slots wider, would it suffice to just make them wider for half their depth?

20

As I see it, looking at the video, Richard is right.
But as I hear… When I hear the sound of the cutting process, it hurts my ears.
I hear a quite unhappy cutting process. I hear resonances, vibrations.
This maybe affects the stability of your strategy mounting the stock to the base.
Can you give more information on how you fix the stock?

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