Need help understanding spindle specs

[Roy Harding]

For the MOST part, I set the spindle speed at 12K (200 on the dial), and adjust X/Y movement speeds for the individual bits appropriately.

I found that I'd often forget to change speeds when I changed bits - but having the appropriate X/Y speed in the tool database meant that I never push a bit to the breaking point.

[Chelmite]

Hi. Does anyone have an answer to my original question? For a given RPM (12000, 15000, or 18000) what is the HP of my spindle according to the specs on the side of the spindle? E.g., for 12000 rpm (F=200), the spindle label says 0.88(1.15). So, is the HP 0.88 or 1.15?

I'm trying to input the HP/rpm curve in to GWizard to compute the speeds & feeds for my bits & mills. When I assumed that the HP was 1.0 across all speeds, the ShopBot head ended up stalling while it was cutting in the X direction and losing track of where it was. Thinking that it was at X=1.0" when it was really at X=15", the ShopBot then cut through the middle of my workpiece instead of the left-hand edge of the design. I've heard that the problem is using the wrong HP in the speeds & feeds.

[adrianm]

Best to call ShopBot directly for something like that I would think.

Are you sure it's HP you want? I would have thought the torque curve across the RPM range would be more useful.

I've never needed to know the HP or torque of my spindle to work out the correct feed rate. RPM's and chipload is enough.

Are you cutting metal?

[scottp55]

Steve, Admit I'm a newbie(3 months) to the Desktop but confused how feeds and speeds would have anything to do with location unless you're pushing so hard it's missing steps(hasn't happened to me yet). Was unfamiliar with gwizard but after watching their blurb still don't understand how that would affect it. What are you cutting,with what,and what are your settings?

[Brady Watson]

Hi. Does anyone have an answer to my original question? For a given RPM (12000, 15000, or 18000) what is the HP of my spindle according to the specs on the side of the spindle? E.g., for 12000 rpm (F=200), the spindle label says 0.88(1.15). So, is the HP 0.88 or 1.15?

I'm trying to input the HP/rpm curve in to GWizard to compute the speeds & feeds for my bits & mills. When I assumed that the HP was 1.0 across all speeds, the ShopBot head ended up stalling while it was cutting in the X direction and losing track of where it was. Thinking that it was at X=1.0" when it was really at X=15", the ShopBot then cut through the middle of my workpiece instead of the left-hand edge of the design. I've heard that the problem is using the wrong HP in the speeds & feeds.

0.88 hp.

As Adrian mentioned, hp is generally not part of the chipload calculation - Only move speed & RPM are really pertinent - and depth of cut.

My advice would be to put the chipload calc away until you can get the tool cutting without using it. It is very difficult to adhere to recommended chiploads for various reasons, such as inadequate hold down to resist cutting forces, the design is very convoluted with a lot of starts & stops around turns etc. Chipload values are for production - in order to maximize tool life. If you aren't doing production, it is of little use.

If you are cutting aluminum, you should be using a single flute spiral-o upcut bit @ 1.2XY and 13,000 RPM as a baseline. If cutting wood, a good general speed would be 1.5 to 2 inches per second XY, and 13,000-15,000 RPM. If you are burning - reduce RPM or increase feed rate. If it is bogging down or stalling, then slow down feed rate or increase RPM.

LISTEN TO THE TOOL - and adjust accordingly. This will make you a way better machinist/operator than plugging in numbers from some calculator.

-B

[Chelmite]

HP matters because, if you calculate a theoretical rpm and feed rate for your bit, and your spindle doesn't have the power to make the cut, the spindle will stall. I'm not running production, but, if I can get the SB to finish a step in 1 hour instead of 3 hours, I consider that a win. I don't know what you guys do when a job takes more than 20 minutes. I can watch for only so long before I get bored, and I don't want to leave the machine in case something goes wrong.

I'm cutting wood. Did I "LISTEN TO THE TOOL"? Of course. But by then it's too late, because it's cutting the workpiece. I listened to the bit as it was cutting. It sounded way different as it stalled and then tore through my workpiece. I stopped it 3 inches into its detour. Fortunately, nobody was listening to ME when the SB cut through the middle of my nicely routed workpiece. Anyone listening to me would have been able to tell that I was not pleased. (3 of the steps, with different tools, speeds, & feeds worked beautifully. The 4th step, that should have been a trivial outline for the design ended up trashing the work.)

I use a feed & speed calculator so that I get the maximum throughput without hurting the work or my tools. But, the feeds & speeds calculator is only as good as the data given to it. Without the proper HP at the different r's per m, it used the (Marketing) HP (1Hp) as the limit, which I now know it can't achieve. I was running the tool at the theoretical speed of 18,000 rpm and feed rate of 240 ipm, assuming it had 1 HP to back it up, when in reality, at that rpm, it's only 3/4 HP.
(See http://blog.cnccookbook.com/2011/11/...with-g-wizard/ for more discussion.)

By the way, bradywatson's terse answer of "0.88 hp" didn't really answer the question, because (a) it didn't explain the difference between the spec'd numbers inside and outside the parentheses, (b) a previous answer hinted that the difference between these two spec numbers had something to do with the line supply frequency, but didn't say whether this was substantiated, or which number was for the 60Hz supply. I now realize that in my question "the spindle label says 0.88(1.15). So, is the HP 0.88 or 1.15?" I failed to say what line frequency I was using. It's 60Hz.

[Brady Watson]

A number of experienced users have given you valuable advice.

If your idea of gratitude is attitude, then I don't think you are going to get much more help.

-B

[bleeth]

10-4 bw........

[Roy Harding]

H... I can watch for only so long before I get bored, and I don't want to leave the machine in case something goes wrong.

I'm cutting wood. ...

I was the same way at first. Once I got used to it, though - I carry on around the shop doing other tasks while the ShopBot does its' thing. I bought the thing to save me time - and no time is saved if I'm standing there staring at it.

[bleeth]

Once you get used to it doing it's thing it's like watching paint dry.If you're spending the time it's cutting watching it every second you are missing the whole point of owning it. While it works, you should be doing other work, therefore increasing productivity, not just ability.