[Coydog]

Ok here is some pix this is a picture of my experimental Rack belt drive. I Know I saw someone else doing something similar maybe here on CNCZone.
Attachment 207946

and here is that chatter I am talking about. The board in front and the one in back, the cut that is visible was traveling along the Y axis with 40 inch of belt. The board in the middle you can see the Cut that was traveling along the X axis with 72 inch of belt. The chatter mark is clearly visible.

[dbsharp]

I bet that rack/belt drive makes a difference.

[Coydog]

The rack belt I designed did not work well. It did stop the bounce problem of long belt that happens with high acceleration. In my case high is 10-15 ipps. The Rack belt don't stop the chatter marks. My design also have issue with slacking up after less then 30 minutes and introducing back lash into the system.

I finally decided to use the moving knots to see if it was some not noticeable racking that is causing this. The Moving knot system in my case introduced a lot of resistance to the movement of the X which make me loose steps on heavy cuts, but it did eliminate the chatter mark completely. I am now limited to .125 cut depth with .25 bits at 45 ipm.

I will have to gear down my belts drive to get the torque back up to do heavy cuts. Currently The motor is Direct driving the Belts

Pix of the Belt Direct Drive.
Attachment 210740 Attachment 210742

and here is my moving knot pulley

[Coydog]

And here is some of the 1st real project with the machine . I will not get around to putting a belt speed reduction on the machine till after Christmas, but in the mean time got to make some gifts.

The cross is made if scrap pine wood from a Pallet. The Sign is made from Clear Ceder bought at Lowes.

Attachment 210748

[CarveOne]

I don't see any cogging marks in those photos. Did you play with the belt tension to reduce it? They look pretty good.

On my web site in the Downloads folder are the Aztec and Mayan Haab calendar files that lots of us have made if you want a copy. All of the files are free downloads though some of the .zip files are large 3D projects in the Aspire .crv3d file format.

Downloads - CarveOne CNC Woodcraft

[Coydog]

I downloaded your dxf. I think my machine can handle the Mayan Habb at about 13 inch.. The Aztec calender I think is beyond my machine current capability even at 13 inch. I don't have a tool fine enough to cut those detail. My two 90 degree Vbits can make a line about .01 inch on one and about .02 on the other. The point are just not that sharp. but with line that fine it get wipe away with the first touch of sand paper. I got to get some 60 degree and maybe 30 degree bits. I am still experimenting .. The bits I got are just router bits from Harbor freight.

My machine current have a resolution of 0.02 inch per full step. I think my only saving grace currently is the Micro step, My Xylotec board max out at 8x. So in theory I can get 0.003 inch resolution.. but I don't think I get that kind of resolution. I never see belt cogging because it was probably hidden under all the Chatter I was experiencing with my old machine and current one before I outfit it with the Moving knot.

My belts is under about 150lb of tension currently according to my tension gauge. I had it at that tension mainly to control bounce.

[CarveOne]

Good V-cutters will cost $18 to $25 each through Amazon sellers. My own preference is the #1550 and 1540 from Whiteside. The 1540 is a 60 degree 1/4" diameter sharp point that is like an engraving bit. It works really well for very small text up to text that isn't deeper than the flutes. You can see a sample that was done with it in my big machine build log that I posted this morning. The 1550 is a 1/2" diameter 60 degree 1/4" shank that has a 0.005" wide tip. I sometimes use it as a very stiff, very small end mill when doing 3D Celtic knot work. The Harbor Freight cutters aren't especially sharp or run especially true. They work well enough for less precise woodworking uses though. Mine went by the wayside once I started doing the CNC machine projects.

[Coydog]

]Well finally got back to the machine again. Got a chinese made 60 degree V bit and changed the belt from a .387 MXL belt to a G2 2mm belt. Now instead of doing 4.6 inch per stepper motor rev I am down to .95 inch per stepper rev. Bad thing about being broke is cannot afford hobbies . for Carvone I try the center section of the Aztec drawing here are 2 image. The smallest line I can get on 90 degree is around 0.03 inch and the 60 degree is at 0.02 inch. only dif I see is in how deep the line is for the same thickness

This one is cut with 60 degree bits
Attachment 245980

This one is cut with 90 degree bits
Attachment 245982