CNC Router Bit sizes

[kflys]

Hello ,
        My name is Kurt and I am new to Clock building. I have Been building Clayton Boyer clocks by scroll saw and band saw. I also have been working on a DXF file that Clayton Boyer sent me so that I could cut the gears out with my CNC router . I have been having problems with when I run the file that I created with Cut2d to cut the parts that the parts are getting cut to short on the gear teeth profile. when I run it in Cut2d's preview it looks like it is going to cut OK but not when I run it my CNC router. I am using a 1/8 up spiral bit and I am just wanting to know what type of bits you guys are using to cut the gear teeth?  I plain on start to learn gearotic so I can make the gears using that program. Any help with this would be great!     

[ArtF]

Hi:

  It sounds like your cutting on the profile, but the toolpath needs to be offset by the radius of the bit. I use a 4mm or 6mm bit for most of
my cuts, but the smaller the gear of course the smaller the bit. Generally, the bit must fit between the teeth without overlap.
If your not offset enough things will look good till you cut, then you get short teeth with large gaps between them.

Art

[marklazarz]

Art had a good suggestion.  Make certain that your profile cuts are cutting on the outside for the gear teeth and on the inside for internal spokes and bearing hubs.  I use an 1/8" bit generally around 18K-20K RPM and 35-40 IPM feed, 30 IPM plunge using 1/2" ramps.  If you use a nice sharp bit, the tear-out on high quality Baltic Birch plywood will be minimal.

Mark

[John T]

  I started out at 1/8" but really only produced more sawdust so I went to a smaller bit, and it is better for me.  I have used a wide variety of bits but really my current favourite is a 1/16" router bit.  When you first look at it you'd think that it couldn't possibly give a smooth cut but it does.  If I'm doing a 2.5D  bass relief than I use round tipped end mills of the same diameter.

Gearotic does a perfect job of deciding what should be an "inside" cut and what should be an "outside" cut so that your gears turn out  really nice and as expected.

My rpm is unknown but I'd guess at 2 - 3000 rpm.  My feed rate is nominally at 100 its but the way my stepper motors are set up they never get up to that speed there's just too many changes of direction in the gCode.  My depth of cut is only 0.70 inches because my motor on my spindle is really from a radio controlled toy with 45 turns.  It uses 12 Volts.

Maybe this will shed some light on what some other are using

John

[marklazarz]

My feed rate is nominally at 100 its but the way my stepper motors are set up they never get up to that speed there's just too many changes of direction in the gCode.  My depth of cut is only 0.70 inches because my motor on my spindle is really from a radio controlled toy with 45 turns.  It uses 12 Volts.

John

0.70 depth of cut with a 1/16" diameter bit?  I didn't think that was possible at a very slow speed much less 100 IPM.

Mark

[Dan Mauch]

Are you sure the depth of cut is 0.70?. The usual rule of thumb is that the depth of cut is 1/2 the diameter of the bit. 0.070 is more like what it should be.
Dan Mauch

  I started out at 1/8" but really only produced more sawdust so I went to a smaller bit, and it is better for me.   I have used a wide variety of bits but really my current favourite is a 1/16" router bit.   When you first look at it you'd think that it couldn't possibly give a smooth cut but it does.  If I'm doing a 2.5D  bass relief than I use round tipped end mills of the same diameter.

Gearotic does a perfect job of deciding what should be an "inside" cut and what should be an "outside" cut so that your gears turn out  really nice and as expected.

My rpm is unknown but I'd guess at 2 - 3000 rpm.  My feed rate is nominally at 100 its but the way my stepper motors are set up they never get up to that speed there's just too many changes of direction in the gCode.  My depth of cut is only 0.70 inches because my motor on my spindle is really from a radio controlled toy with 45 turns.  It uses 12 Volts.

Maybe this will shed some light on what some other are using

John

[kflys]

Any idea where I would change my Offset in the software?

[kflys]

Also where do I buy Good end mills cheap?

[Mooselake]

Cheap and good often contradict each other.  That said, I've had good luck here, especially if you watch out for their sales and closeouts.

Look here for good advice on what to do after you get those endmills.  They used to (and probably still do) have a tutorial on how to determine feeds and speeds, but one of their techniques was going until you break one and backing off.  Precisebits sells good bits, but they aren't cheap.  I am, so I mostly stick with the Drillman.

Kirk

[John T]

You guys are right I take 70 thousands cuts.  sorry