Indexing Holes - Drill or hole machine?

[Scalesoar]

Folks, I need a little guidance on creating index pin holes in my CNC Router MDF table surface.

I intend to place numerous 3/8" diameter holes in the surface for indexing and insert steel 3/8" pull-pins for location.

Is the best method to drill the holes using a standard drill or to use a smaller router bit (1/4" 2-flute end mill) to machine the holes using a helix cut to depth? Can I get the accuracy for no slop using a 3/8" Drill?

Thanks
Tony

[sploo]

I'd strongly suggest using the machine itself to cut the holes, so the easiest way would be to draw a grid of circles with a CAD package, and then use your CAM package to pocket cut each one (with the 1/4" bit).

Even better would be to use a 3/8" bit, and place a point at the center of each hole, again using your CAD package, then create a drilling process in your CAM tool.

I use a free CAD package called ProgeCAD, and a cheap (but very good) CAM package called SheetCAM. Either of the above is easy with these two (and probably many other packages, to be honest).

I wouldn't recommend using a drill bit - especially if you are thinking of using it in your spindle. Drill bits aren't designed for use at spindle RPM speeds.

[sld4121]

Spot drill, drill undersize, and ream your holes to size for a perfect fit. Solid carbide drills will certainly help, but their is no guarantee without reaming that you will have your perfect "no slop" fit.

[Scalesoar]

Appreciate the feedback. Two different approaches and obviously both viable. I would prefer to machine using pocket methods because this will be quicker but drilling and reaming also meets the need!!

Hmmm - quandry! I think I will try a test hole with the pocketing method to see how close I can get it. The pins are ground, hardened steel draw pins (taped down the center for easy removal). If that doesn't work - i will drill and ream them.

I have a 200V 4HP spindle on a Yaskawa VFD - programmable (via software) and adjustable down to 1000 RPM. With a good quality drill bit, this would work. Not sure however about the reamer. I was under the impression that reamers need to go real slow.

Thanks for the input

[Geof]

... Not sure however about the reamer. I was under the impression that reamers need to go real slow.

Thanks for the input

A reamer in MDF is not very useful. In addition you will probably need blind holes to avoid pushing your pins all the way through; it is not practical to ream a blind hole. Interpolate the holes with a 1/4" carbide if your machine has enough precision or pilot drill and then straight plunge with a 3/8" carbide. For the straight plunge you need to make sure the cutter is running very true otherwise your hole comes out oversize.

[Scalesoar]

Geof, pilot and plunge - didn't think of that one and your comment about spindle true is noted. These are blind holes! I think interpolation/pocketing is in order. I have my direction - Thanks!!
Tony