Maximum materal thickness on PRT 96?

[Sawdust-and-Noise@sympatico.ca]

How do you make a cut 5" deep (a 3/4" wide slot with a 5 1/2" long 1/2" bit for example) with a standard setup PRT 96 where the slot is located in the middle of the material, and not gouge the material arround the area to be machined?

6" gantry clearence, 7" travel = only 'bout 1 1/5" - 2" clearence between the bit and the table! Help.

[gerald_d]

Guy, just thinking outside the box:

- Drill a 5/8" hole, drop the bit into it, move the router over the bit and then chuck together
- mount the job under the table, if you can live with a slot through the table
- mount the job on the end of the table.
- move the Z carriage higher up in the y-car
- use progressively longer cutters

[toml@starband.net]

Why not machine everthing BUT the slot and then do it on another machine? This would be a normal and easy thing to do on a standard Bridgeport Mill.

[rgbrown@itexas.net]

Guy,

Gerald has described the methods I would try. I have a couple of questions and observations.

Where do you get a 1/2" bit long enough to cut a 5" deep hole and still have it firmly gripped in a chuck collet? I have some 4" cutting edge bits and they scare me.

If you mount the project below the table and plan on raising it in steps think of how you are going to raise it and have it "registered" for the next cut.

Ron Brown - rgbrown@itexas.net (mailto:rgbrown@itexas.net)

If Stupidity got us into this mess,
then why can't it get us out? - Will Rogers

[srwtlc]

How about a shorter, safer bit and cut just past halfway then flip the stock over and come at it from the other side. If you register it properly you should come pretty close. I would think that with a bit that long you would have as much runout on the bottom pass as you could be off the mark by coming at it from both sides.

Scott

[Guy Hilliard]

I'll probably end up going for moving the Z axis higher on the Y car. Thanks all.

Is there a 12" option on Z travel? 'Cause I think that would work too!?

[ron_cleaver]

A guy from Onsrud once told me that the cutting length of a bit should be no more than about 3 times the shank diameter. You can have all kinds of problems if you don't adhere to that - wobble, runout, broken bits...

[dmdraper]

The three times shank diameter thumb rule was also mentioned by the Colombo spindle rep at the Jamboree last weekend.

[ramdesgn@ionet.net]

Guy,

Another way would be to lower the 1/2" bit through the material, come back up to the first level of cut, say 0.75", repeat the path in ingremental steps to the final depth allowed.

Remove the pattern and cut the remaining material on a table mounted router using a 1/2" flush trim bearing bit with a 1" or longer flute.

Your final may now need a little sanding for the acceptable product.

Dick McGuire
ramdesgn@ionet.net (mailto:ramdesgn@ionet.net)