5x8 PRSalpha (vacuum and spindle question)

[Jackson Ampworks]

Hello guys! I'm new to the forum and have a ton to learn so any patience would be greatly appreciated. To give you some background on me I own a guitar amplifier manufacturing company and over the years business has grown to the point to where it makes sense for me to bring the cabinet work in house so here's what I'm looking at.

I use exclusively baltic birch plywood for my cabinets; primarily 3/4" with some 5/8 and 1/2" mixed in. I'm looking at the PRSalpha 5'x8' as it will let me use 5x5 sheets of plywood which is so much cheaper than a 4x8 sheet of the same material.

I've been looking around and I have not found the specific answers I need so thought I'd just ask my questions directly.

1) Since I'm going to get the 5HP Spindle and ATC I wanted to confirm that the 5HP spindle has enough juice to rip through 3/4" baltic birch in one pass at reasonable speeds.

2) I'm getting the vacuum table but wanted to make sure that I size my pump correctly. For 90% of my work I'll only be using 5x5 of the bed so I'll be able to cover the remainder of the table to keep the vacuum but I really have no interest in tabbing, onion skinning or multi-pass cutting my parts. I need to hit it and get it done as fast as possible. Any recommendations on which pump to get? I'm all for saving money on this so I'm totally open to getting a refurb unit. I am limited to single phase units as my complex doesn't have 3 phase.

3) I will also want to invest the time to round over my parts on the CNC to save me the step of having to do that manually. Any gotchas I need to know about there? I was concerned that a round over bit might move the part easily if my vacuum is not where it should be.

Thanks for any help/council you can offer!

[benchmench]

Brad,

Welcome to the forum! The answers to many of your questions are already here and can be found by searching on the terms you are interested in.

The 5hp spindle and Shopbot PRS Alpha can certainly cut through 3/4" Baltic Birch in one pass. There are also other variables of the "cutting" formula that will be affected if "1 pass" is the requirement. This puts more cutting force on the material hold down and, depending on the cutting speed of the gantry, more force/friction on the bit and material. In other words, the machine will cut it in 1 pass but the material may move or have an undesirable edge.

Since you don't have 3 phase power, you will have to go with a single phase solution for a vacuum table. There are many methods described here on the forum but this usually involves a Fein or shopvac solution rather than a regen blower. Most Shopbotters make their own vac table according to their needs. We all have to work within our limitations, so onion skinning, tabbing or multiple passes may be required if you don't have enough vacuum to hold the part.

Regarding roundovers, these can be done on the CNC, however, the profile and dimensions of the tool will need to be described to the software. Some care should be taken to minimize the sideways cutting force to the spindle shaft since this can cause premature wear on the bearings.

Best of luck!

[cabnet636]

I have a 15 hp regen with 95% of the hold I need, I am cutting .75 birch in two passes because I have small parts which tend to give loose far quicker,,, I would get the largest vac I can.. if it is all large parts then this would be a plus +

I would consider cutting all parts to say .70 then a final quick pass starting at .70 and cutting .055 deep for cut out,, this way the vac holds well and long with no release and has virtually no pressure on parts for the last pass. to me speed is in proficiency not throttle

[dlcw]

Brad,

I cut Baltic Birch all the time with my 5x8 Alpha using a 2.2HP spindle. I first cut in a climb direction leaving a thin skin against the table. This serves two purposes - keeps all the parts stuck to the table for the final pass and sets me up for the conventional direction second pass.

My second pass only cuts the 1/32" skin and puts the final cut EXACTLY on my cut line.

If you cut full depth in one pass, the bit flex and machine flex will most likely push the bit away from the line creating slightly oversized parts. I learned this the hard way right after getting my machine.

I cut Baltic Birch with a 1/4" mortise compression bit. This gives me a super clean top and bottom cut with no tearout.

For vacuum holddown, since you don't have 3phase power, I would recommend setting up the Black Box vacuum setup developed by Gary Campbell.

http://www.talkshopbot.com/forum/showthread.php?t=11813&highlight=Black

I've been using this for a couple of years now. The only problems I have is when I'm cutting prefinished material (plywood, Baltic Birch, etc.) Since these materials are so slippery, I sometimes get a little shift in small parts. But unfinished material sticks to the table like it's been glued down. I have a 7 zone system that is optimized for 4x8 and 5x5 plywood material.