Cutters, speeds for baltic birch

[richards]

I'm strongly considering buying a PRT120-60 with PC router, but I need some advice before I buy the machine.

For my main project, I need to cut panels from sheets of 3/4" thick baltic birch plywood with each panel having a perimeter of about 100 inches. Since each panel will get a final round-over edge with a hand-held router, edge finish is not a big concern; however, reasonable cutting speed and reasonable tool life are important. Using a 1/2" cutter (probably 2 flute solid carbide compression spiral bit) can I expect a cutting speed of 80-100 inches per minute with two passes per panel, one pass cutting about half way through the plywood and the second pass the same, except for using the tabbing command so that the panels don't come loose? How many inches can I expect a solid carbide cutter to last?

Right now, cutting the panels with table saw, band saw, shaper, and several router operations is too labor intensive. I'm hoping that using a shopbot to do most of the work with a hand-held router to do the round-over would make the whole project economically possible.

[elcruisr]

Well, I cut with a 5hp columbo spindle but I've cut thousands of 3/4 ply sheets with it including a lot of baltic birch. I can easily single pass sheets of 3/4" ply. For tooling the 3/8" single flute compression spirals from Onsrud are giving me the best results. The speeds achievable with the shopbot really don't require more flutes or diameter for this type of material. If I was cutting at, say 2"/sec I'd keep the rpms down at 9,500 to 10,500. This would give a good edge as well as good tool life. You can run higher rpms but it will result in dust not chips and that means a hotter tool and shorter cutter life. I find on production runs like this a new bit will last about 12 to 14 hours of production time and a resharpened bit around half of that, we also find resharpened bits usually need to be run a little faster to get the best edge qualities. We resarpen two to three times and then replace the cutters.

If this application will require real production runs then spring for the spindle. You'll wear out the router 6 times over or more before you rebuild a spindle and you'll have much better rpm control and cut quality. We often run ours two shifts a day.

Eric

[richards]

Eric,

Thanks for the quick reply. Refiguring things, following your recommendations, shows that the project is not only possible but also profitable. It looks like the next step is to talk to the bank.

[elcruisr]

Michael, it would also be worth your time to call Shopbot and see if someone is running a 'bot similar to what you want somewhere near you. Most 'bot owners would be glad to show you one in operation. It would give you a really good idea of what it takes to set one up and get it running. If you're anywhere ner central Fl I'd be glad to show you mine!

Eric

[richards]

Eric, thanks for the offer, but Salt Lake City is a long way from Florida. There are a few ShopBot owners that I've heard about that have shops within 300 miles. I'm hoping at least one of them has some experience doing what I need to have done.

Even though I've had quite a lot of experience using hand routers, I've never pushed them. All of my cuts have been light and slow; however, after reading some of the posts in this forum, I decided to take some deeper, heavier cuts. Surprize, other than a LOT more noise, the cuts were just as accurate AND the bits stayed sharp longer.

My main work for the last twenty-five years has been designing process control computers and writing software to operate them. Knowing how touchy stepper motors are (and how often manufacturers use optimistic ratings on their equipment), I assumed that estimating production based on 50% of the equipment's advertised capacity would still be wishful thinking on my part. Your original reply showed me that what I wanted to do was not only possible, but quite conservative.

I do expect a steep learning curve, but I've had quite a bit of experience with CAD programs -circuit board layout and AutoCad drawings for mechanical parts to make the process control computers work. My main concern was throwing the better part of $20,000 away on equipment that was more suited for a hobbiest that wanted to play at woodworking for a few hours on the weekend. Apparently I was mistaken. Anyway, after a few phone calls tomorrow and a short trip or two, I should be ready to make the purchase.

I do have one more question about the Colombo spindle. I don't have three-phase power in my shop. Is your spindle single-phase or three-phase? Do you have any concerns or suggestions about using the single-phase spindle?

[mrdovey]

I don't have three-phase power either; but my single-phase Colombo does just fine. I gave it its own 230V 30A circuit and haven't had any problems.

Morris

[elcruisr]

I do happen to run three phase power in my shop but there are plenty of people running single phase spindles. It's just a matter of which model of control box you get to run the spindle.

By the way, the manual that comes with the control box is about useless as it's written for engineers, not operators. However, a quick call to the tech support at Shopbot will give you all the info you'll ever need to use it.

I'd say we have over 50,000 parts / 2,000 sheets of 3/4" ply cutting on our spindle so far and the bearings are still going strong. One thing many people don't catch is to do a ten minute warm up before starting and a ten minute cool down before shutting down completely for the day. I've talked with the factory techs and they tell me this can double or triple the bearing life. The bearing tolerances are a few ten thousandths and designed to be hot before being loaded up!

Feel free to give me a call at work if you want more info.

Eric Lamoray
Balsys Wood Arts, Inc.
407-654-7611

[gerald_d]

Eric, given Michael's concern about loading the stepper motors, maybe you should tell him that your stepper motor arrangement is not standard? (If I remember correctly, you have doubled your y-motor?)

[elcruisr]

Yes, I have a double y-motor, that is a standard option from Shopbot. We went to that for increased accuracy. According to Shopbot the motors are more than capable of running the x and y axis alone. The double motors just tightened things up for us a little better on our 5' x 12' machine. They are using motors that are being run well below their limits, the limiting factor is really the driver board. If I remember right the driver boards are only capable of pushing a little over half the capability of the motors. (Correct me if I'm wrong Ted?)

Eric

[prosigns]

I do have one more question about the Colombo spindle. I don't have three-phase power in my shop. Is your spindle single-phase or three-phase? Do you have any concerns or suggestions about using the single-phase spindle?
*
Morris Dovey
P

Morris
I get 3 phase power with a Woods 3 phase inverter I purchased with a Perkse spindle. I went with the inverter after checking into what it would cost to get 3 phase to the shop. Been using it about 8 yrs. now and it still works fine. Spindle brearings are still tight enough to cut aluminum & steel although it is usually used for woodworking.
Gary