Spindle speed & feed rate on a Taig

[Stuff-Builder]

Hi everyone,

I bit the bullet and bought a Taig 2019CR last week. I wanted to be able to make brackets and whatnot accurately. I got the steppers on and hooked up and everything moves fine (steppers get fiercely hot though). What a lovely toy!

I made some initial cuts last night on a piece of 1/4" aluminum, using a 3-flute 1/8" end mill. I think my spindle speed was 1650 rpm, and I was cutting .030" deep slots at 4"/min. Seemed to cut through it all just fine, but that doesn't mean I wasn't nervous!

Some things I've read say that I should be feeding faster - like 8"/min, taking a deeper cut (half the cutter diameter), or both. Things were chattering some, but my setup sort of sucked. I'll clamp things better next time.

Am I in the right ballpark here?? Any advice would be greatly appreciated!

Thanks,
Scott

[Mcgyver]

Congrats on the machine. Over time this will become intuitive, but here’s the process…
1) this is all theoretical, its a rare home machine that can remove metal at theoretical limits, a practical stop either on rigidity or power kicks in first
2) determine cutting speed - function of cutter and work material, expressed in feet per minute - hss cutter into AL is about 400 fpm - this number is a plugged number, looked up from a reference like machinery's handbook.
3) from that determine spindle speed. its the max surface speed for the periphery of the cutter in that material/cutter combo
4) based on how big a chip per tooth you want to cut (maybe a thou or two for a small cutter like that, figure out the advance rate in inches per min.

I’m too lazy to do all the math, but those are the steps. you will likely not get to a theoretical maximum before the machine gives up - think of it as the machines limitation in horsepower and rigidity to remove only so many cubic inches of material per minute.. As something is going to be set less than max, I like to see a reasonable chip size and the spindle slowed down as this increases cutter life (its not a linear relationship).

if you are getting chatter, backoff on feed or speed or as you've noted use a more sturdy set up. overall, the numbers you posted sound reasonable - it worked didnt it?

[Stuff-Builder]

Mcgyver, thanks for the input. Yes, it did make some chips! Pretty, perhaps not, but nonetheless.

I've got some more info from some other Taig users, and I'm going to try more spindle speed, put together a better clamping arrangement, and give it another try. I was in the right ballpark, though.

Has anyone used 1/4-20 carriage bolts on their Taig table? Looks like they'd fit perfectly with just a little filing on two sides, but I'm worried about gouging the slots on the table when I tighten the bolts. No big deal?

[Stuff-Builder]

Well, I did some more playing around the other night, with better results. I tried the following:

3/16" Three flute cutter
4200 rpm Spindle speed
5 ipm feed rate
Slotting Aluminum plate at a depth of .040".

The chips cut much cleaner and didn't leave any nasty burrs or gunk (technical term) on the edge of the cut. A little oil seemed to help too.

I experimented with a .005" climb-milled finish pass and this didn't seem to make any difference.

I also played around with an 1/8" cutter running at 10,600 and that left an ugly cut.

Fun stuff! I'm definitely getting braver with the mill.

- Scott

[jkeyser14]

Glad you're enjoying it. I considered using 1/4-20 bolts myself, but didn't want to scratch the slots. Instead I just machined some t-nuts and tapped them for 10-32.

This approach works fine, but requires holes in all your stock in order to mount it to the table. After seeing the TS Engineering vice however, I think I'm going to purchase one of those. It should remove the majority clamping problems that I encountered and allow for quicker setups.

TS Engineering Vice:
http://www.home.earthlink.net/%7Ermteo/tseng/id8.html

Also, .005 is not much material for a finishing pass. I'd leave about .015 so that the bit actually has some material to remove. And from all of my experience with machining, climb cutting definitely produces a much nicer finish on aluminum, and sometimes doesn't require the use of a finishing pass.

[shovelitdeep]

Stuff-builder
Glad your machine works. I was going to recommend light oil-cooltool works well on aluminum. You may not want to climb mill after your machine wears in a little, it causes broken tools because the tool will eventually grab the part and pull the table towards itself, suddenly increasing the chip loading by whatever the slop in the system is.
The thing with these machines is: you can't be in a hurry.
Have a good time with it
Rich