Spindle speed

[Geerbangr]

Hey guys!! I have a small job to do on aluminum and I’m wondering about spindle speed. Spindle speed=3.82xsfm/diameter.

So that equates to 1528 rpm using a 1” bit. Here’s the problem, my closet spindle speed is 1100 or 1900.

So with that being said can I cheat the system here and use the lower spindle speed of 1100rpm and slow the sfm down?

I don’t want to use the 1900rpm speed because that’ll burn the bit up, correct?

 

[Downunder Bob]

G'day, you don't say if you are using cutting fluid / coolant. If you're cutting dry I'd slow it down, if using flood coolant you could try the higher speed and see how it goes. I assume you're plunge cutting in one step, probably safer to slow it down you'll get more torque, you don't say what machine, HP etc. When the theoretical ideal speed is in the middle like that it is usually better to try the slow one first, Theoretical speeds are just that theoretical, it's a bit like the speed limit on the road that's the maximum, but you don't have to go that fast. What would you do if it was only 1/2" the theoretical speed would be twice what the lathe will do, so what do you do now, just go with what you have.
Downunder Bob.

 

[Geerbangr]

Hey Bob thanks for the reply. I just have a cheap 20” enco benchtop mill. As far as cutting fluid what would work the best with aluminum? Wd40 or something like that?

I have a 2” wide 2” deep 4” long cut I need to make in a 4” piece of aluminum round stock. I can make several passes so it’s not like I’m trying to cut the max cut all at once.

Is silicone spray good for lube when milling?

 

[Downunder Bob]

Hey Bob thanks for the reply. I just have a cheap 20” enco benchtop mill. As far as cutting fluid what would work the best with aluminum? Wd40 or something like that?

I have a 2” wide 2” deep 4” long cut I need to make in a 4” piece of aluminum round stock. I can make several passes so it’s not like I’m trying to cut the max cut all at once.

Is silicone spray good for lube when milling?

G'day again, I'm not familiar with your machine, and I haven't done any milling for years as I don't haver access to a mill, Plaanning on building a mill attachment for my lathe.

Also on machining Alumimium it's something I rarely do, mostly steel. But I've heard WD40 is good, Kerosine also. Standard approach when in unfamiliar territory start low and slow, and let your machine tell you what it is happy doing.

Your 1100 rpm is good place to start Is your cutter HSS or carbide? Carbide needs to run really fast 4-5 times that of HSS, and requires much more HP / torque. If the cutter is bogging diown halve the speed and try again.

Remember Half the speed gves you twice the torque. keep the feed and depth of cut low and gradularly increase one or the other. If your machine is small, and as you say cheap, you'll probably run out of torque and rigididty before the cuts get too big, but listen to the machine. Let it tell you what it can and can't do, that way you'll learn more about your machine. If the machine is complaining, back off.

 

[Jake2465]

I mess with aluminum almost exclusively. I have seen that doing exterior contouring with a conservative width of cut does not seem to be too problematic, but doing internal pockets that would require a high percentage width of cut is where you could run into trouble. By nature, those cuts seem to produce a lot of heat. without some kind of cooling, I would tone down the rpm and run a feed that would be in the neighborhood of 0.001" chip load.

Working with aluminum is basically a heat game. Milling can easily produce local area heat beyond the melting point of aluminum. In a way it is kind of funny because aluminum is easier to machine than steels but at the same time harder because of the heat constraints. Also, doing deep pockets can pose problems with chip recut which makes it worse.

If you have a piece of spare aluminum that you can sacrifice, then I would try this: give the surface a spray of water or WD-40 (heavy coating is not required) and try out your operation. Have the spray bottle handy and with each subsequent pass, give it another little spray. Also, aluminum hates high RPM and low feed rates. If you start rubbing the tool more than cutting, then the aluminum will turn into jelly and claim your end mills life .

I like to use this online calculator for my chip loads:

http://www.monstertool.com/monster_tool_calculators.html

Hope this helps. Good luck!

 

[mikey]

G, as a general rule of thumb, use the next lowest speed below your calculated speed. BUT as in most things machining, it isn't that simple because your calculated speed depends on many factors and since efficacy and end mill life are greatly dependent upon the correct speed, your calculations are important.

What you are calling a "small job" is a 2" wide X 2" deep X 4" long cut in aluminum - to me, that is a big cut. You indicate that you are using a 1" OD end mill in a benchtop milling machine. That is a big cutter being used in a machine that is somewhat limited in rigidity and power. Most cutting guidelines and calculators do not take the mill into account; they assume you have all the power and rigidity needed to make the cut so if this is not your reality then you need to make adjustments and slow down.

I assume you are going to plunge cut the center and then widen the slot to size. If so, then you are making an initial slotting cut and then two profiling cuts. Slotting and profiling cuts have different cutting speeds. For slotting cuts, it depends on your axial depth of cut. For profiling cuts it depends on both your axial and radial depth of cut. Granted, this fine differentiation may not matter much when all you have to adjust speed is a pulley system but on a variable speed mill, it does make a difference.

Add to your depth of cut, your feed. If you have a DRO and power feed then you can calculate your feed in IPM. If you do not have a DRO and/or are cranking manually then you will need to do it as Bob indicated above - feed by hand and feel for a slight resistance to the feed.

Since your question is about speeds and not about how to use an end mill, I am attaching some guides from Niagara Cutters that will be useful. It addresses the speeds used for various radial and axial depths of cut for different materials. Have a look.

The other thing I wanted to add is that for this kind of job, a roughing end mill is more useful for hogging. Your finishing end mills will last much, much longer if you use roughing end mills to debulk the stock first. I would use a coarse pitch rougher for this job and also use a stream of compressed air to clear the chips and cool the cut. Oil/WD-40 is okay but it tends to clump the chips and makes it harder to clear them so I prefer air for slotting cuts in aluminum. Note that speeds also vary for both roughing and finishing end mills.

Good luck!

 

[Geerbangr]

Thanks for the replies fellas. I have not yet purchased the cutter I’ll use to do the job. I’m sure you guys can tell I’m pretty green at machining. I do have a dro and I do have auto feed that I will install for the x axis. So with those file links Mikey that should help with the process.

My plan is to use a roughing bit to hog out the heavy stuff then complete the job with a finishing bit.

 

[Aukai]

Just on a side note, are you a YB member?

 

[Geerbangr]

That’s me!!

 

[Aukai]

Don't tell them your here then LOL