Not enough room to cut now my puck is done!

[harryball]

I thought I'd done so good too, take a look...

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I used 3/4" MDF and surfaced both sides. I then cut pockets into the top side to allow for air flow. I added a sheet of laminate to the top and machined holes and an outline of the part that would be cut and applied the gasket material. I had to use 2 layers of 1/16" gasket. I should have ordered 1/8" soft.

It works! It holds the cedar board in place and I can't budge it. Then the bad news, I don't have enough room under my Z axis to machine the parts. From the top of my steel to the bottom of the collet nut at full reach I'm at about 6 7/8". Once the vac-table, spoilboard, puck and blank are added I have roughly 1/2" left of Z travel. There is no way I'll get the dust skirt on. Worse yet... the spoilboard is already surfaced down almost 1/2" so with a new spoilboard it won't fit at all.

Ideas?

Robert

[Towersonline]

Can you raise the rails by placing spacers between the V-rail and the Aluminum rail?

It looks like there is about 2 inches of your spindle collet is hanging below the y gantry. You should be able to raise the Z axes up a bit.

Bill Thorpe

[harryball]

I don't remember the specs on the PRT Alpha and I don't see them in the manual, can't find my spec sheet either so I'm not sure what it is supposed to be. Best I can figure the distance from my table top to the collet nut is about 4.5" to 5" at the best. For some reason I thought it should be better than that. I know Bill Palumbo suggested using 3" foam with a 3" taper bit to carve his "ladies" but I couldn't even fit that in.

Could someone tell me the spec on the PRT Alpha so far as nominal cutting depth?

The Z will not raise higher right now because the frame strikes the Z spring hooks. Does anyone know, before I go unbolting stuff, if the 4HP HSD spindle can be moved up a set of holes? I don't know how that would affect the dust skirt.

I considered removing the spoilboard but I really don't want to do that either as my current one is glued down per forum suggestions. If I surface it away and start over I don't know how I'd keep the new board flat while not gluing it.

Stumped for the moment...
Robert

[paco]

Last week I machined in 5.5" thick polyurethane foam with a 4" long out of the collet tool AND a 2" thick support/spoilboard assembly... I must admit that I had only 0.3" left for safe Z and home position thought!

There's "always" a way.

No, I didn't raised the rails nor the gantry.

Bot on!

[harryball]

So you have 2" + 5.5" + 4" + .3" = 11.8" from the collet nut to the steel of your table?

Why do I only have 6 7/8" from the steel to the collet nut then? What is spec anyway?

Robert

[fleinbach]

Robert,

I have 10 1/2" from my collet nut to my steel supports. My X-car frame is 9 1/2" above the steel cross member so the collet nut is traveling 1" up into the X car cross memebers. But my table was built by me.

[Brady Watson]

Robert,
Way back when, I took a piece of 2X3X3/8" wall steel tubing and made a riser for the gantry. I also replaced the utility strut with 1/8" wall steel tubing and welded the whole deal. This gave me 2" more (about 8" total) on my PRT so that I could have clearance for the indexer.

Now I have a PRT Alpha gantry on that machine and it has about 7.5" of clearance with the factory setup (to top of spoilboard). This gave me enough room for 3" material and a 3" cutter + 1.5" of safe Z. If you wanted to raise it up, you could just make steel plates that attached to both sides of the X car where the v-roller guide wheels are. You might also be able to put a riser in there like I did on the PRT...I haven't had the need to do it on my Alpha, so I can't give you an exact formula. Another option would be to put spacers under the X rails to boost it up. Thick walled AL tubing (structural) works well for this and you can cut it on the chop saw...or buy spacers from McMaster-Carr etc & longer bolts.

One thing that you can do right away if you haven't already, is move the Z axis up as far as it will go by bolting it thru the gantry at it's lowest 4 holes...Figured I'd mention it in case you overlooked it.

-B


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[harryball]

Thanks! I got off the phone with Chris at SB and he pointed out the Z axis adjustment. (doh!) I was in the middle 4 holes. I'm now in the lower four and have plenty of room. As soon as I re-square the Z it looks like I'll be good to go.


Robert

[harryball]

I made the adjustment and did my first test cut. The only problem I have is no room for the dust skirt. If I try to raise the bit up high enough to clear the material the bracket on the dust skirt hits the rail underneath. I can't lower the skirt anymore either, the set screws won't engage the vane on the Z axis.

I was trying to figure out how to turn the foot 180 degrees. Has anyone come up with a way to do that easily? Seems a bracket mounted (somehow) to the front of the spindle that would let me mount the dust foot holder with the 2 set screws would work perfect.

Robert

[harryball]

I'm happy to report that this project is now running in production. I'm machining 2x8 cedar into bat house sides using the bot rather than my previous manual method.

The boards are cut to 48" lengths and surfaced on one side using the bot. I drop the board on the vac jig (shown in first post) and run a custom routine that surfaces 1/8" of the board away. The board is then run through the planer to bring it to a total thickness of 1.25"

I've had a few issues with cupped boards or a slight twist not allowing the vac to seal before surfacing. So far flipping the board over has worked in ever case. Once surfaced on both sides it sticks and holds from 15" to 20" of vac. This varies for each board. I found some of the small knots will leak slightly. I place the board and turn on the vac, make sure it sticks then wait until I see the gauge stabilize before proceeding. Takes less than 20 seconds to know if it's going to hold or not. Once I know it's not moving I run the cut file.

I'm cutting with a 3 flute 3/8" roughing bit at 10k RPM and 5 ips in 2 passes! It cuts the cedar like butter. I've varied the settings slightly but at 4 ips and 10k RPM I was getting a lot of screaming from the bit. At 6 ips and 11k RPM it was just too scary, I'm not in that big a hurry. On prepared stock it takes about 15 minutes to machine enough parts to build 6 bat houses! Including the time to prepare the stock I'm still at less than 30 minutes total time from boards to parts ready to use. While not as "hands free" as milling other parts because I have to swap boards fairly often, plane, set the vac etc... it is a real time saver from doing them manually and the quality is consistent.

If anyone has considered making a hi-vac holddown with something like this large custom jig or small pucks... stop considering and do it, the hold down force is amazing. It's so easy to work with I should have done this sooner.

Robert