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Probotix - Feed & Plunge Rate help needed

2K views 8 replies 5 participants last post by  Marco 
#1 · (Edited)
Hi guys, I'm a total newbie to the world of CNC Routing here. A co-worker of mine recently purchased a Probotix Comet and he has all but given me the reigns to it. I'm very experienced with AutoCAD and SolidWorks but this is my very first experience with CNC. He has Cut3D on his PC and I've become pretty proficient with importing my .stl files into it and setting up everything. However, I'm struggling with getting feed and plunge rates dialed in on my roughing and finish cuts. I've googled this quite a bit but most of what I'm finding pertains to metals and not wood. Can someone offer suggestions as to what would be a good starting point?

I'm using the same bit for roughing and finishing so I can easily maintain 0 as I'm doing double-sided machining. Like I said, I'm brand new to this and am trying to keep it as simple as possible for now. I'll list as much information as I can below.

EDIT: Forgot to include the router being used in the machine is a Bosch Colt and it is currently set on #4 setting.

Roughing Pass:
Bit: 1/4" ball nose end mill (2 Flute)
Wood: Cypress - 12" X, 3" Y, and .6" Z
Pass depth: .2"
Stepover: .1 (40%)
Feed: 1.0 in./sec.
Plunge: .5 in./sec.

Finishing Pass:
Bit: 1/4" ball nose end mill (2 Flute)
Wood: Cypress: 12" X, 3" Y, and .6" Z
Pass depth: .125"
Stepover: .0225 (9%)
Feed: 3 in./sec.
Plunge: 3 in./sec.

Do these #'s seem acceptable as far as a safe place to start is concerned? Either way, I'm all ears!

Thanks,
Jason
 
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#2 ·
My 2 cents worth.

Why would you do a rough pass with a ball nose??? The whole idea of a rough pass is to get rid of excess material. Use an end mill for this. Depending on wood hardness, I usually run .1 to .2 per cut when roughing.

On my Nebula I usually run 130-150 ipm with good results.

HJ
 
#3 ·
I'm using the same bit for roughing and finishing so I can easily maintain 0 as I'm doing double-sided machining. I am trying to keep it as simple as possible for now.

The material is .6" thick and finished product is .375" thick so there's not much to get rid of honestly.
 
#5 · (Edited)
There are three basic ways to get feed rates that will give you results.

First is trial and error where you run faster / deeper until the bit breaks or turns black and then keep moving lower. You may never get a optimum result.

Second is to contact a router bit supplier that will give you some basic guidance. They will give you a point to start at with their part number and hp of your router. Do not assume a similar bit from different manufacturers will perform the same. The underlying factors related to chip load, flutes and flute angle are all factors.

Third is to use a calculator where you input all of the variables. There are up to 30 variables needed to get a "perfect" feed rate, which you probably don't need, just 90% is great. Even wood density is used for some. I don't know of a full "freeware" calculator that is complete, but all the underlying formulas are available. I tried combining the formulas in an Excel spreadsheet, but there was always one more step to get included. One I am using is Gwizard and hasn't let me down yet. It even has a pull down to choose the species of wood for hardness. G-Wizard CNC Speeds and Feeds Calculator: Market Leading

Steve.

OK, fourth option. Probotix is a good company with a lot of knowledge in these size machines. Have you called or emailed them for a starting point?
 
#7 ·
During 3D cuts the feed speed rarely gets up to the programmed feed rate as the bit has to slow down and speed up too much. I generally set my speeds at 200ipm and plunge rate at 60ipm (the machine hardware limits) and then use the feed rate slider in LinuxCNC to slow it down if it appears to be cutting too aggressively. If your 3D cuts are doing a lot of up and down movement then increasing the plunge rate (for the Z axis) can help shorten cut time considerably.

4D
 
#8 ·
Thanks 4D! I was hoping you would chime in after reading some of your other posts regarding Probotix machines. I didn't even think about slowing down the feed in the LinuxCNC interface. I might have another question or two for you before long. LOL!
 
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