RPM starting point

rzw0wr

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I have seen the formula for speeds and feeds.

They ask for SFPM, no problem there.

Feed rate. Big problem for me.
I have power feed however it is not calibrated or in other words it does not let me know what the feed rate is.
The power feed has a rheostat that I turn to what ever.

Is there a best guess for a RPM for a cutter diameter to start with?


Thank you,
Dale
 

Hawkeye

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I made this set of tables up when I was getting started. It's just a general guideline, but still seems to work for me. You can ignore the bottom right table - it doesn't apply to your lathe.
 

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Jubil

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HM has an app you can download. Machining calculator is what it's called. Search this forum, it should come up.

Chuck
 

dpb

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You can time handwheel rotations under powerfeed, and construct a chart of speed per dial position.
 

rzw0wr

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I forgot to mention that I was referring to a mill.

Nice app though. I can use it on my lathe that has power feed

dpd, I tried your suggestion. The power feed is not that good.
4 ipm is the same mark as 2 ipm or very close.

I just look at the handle and guess.

Thanks for the replies,
Dale
 
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mikey

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Is there a best guess for a RPM for a cutter diameter to start with?
In a word, NO. As usual, the real answer is that it depends. Cutting speeds vary with end mill type (HSS, carbide, roughing or finishing end mill), axial and radial depths of cut and the material you're working with. The rigidity of the mill and available horsepower also figure into the mix. All of these things affect the feed rate you use.

Most charts and formulas are for industrial mills and high quality end mills, not hobby machines. You need to find some ballpark numbers and then back off on the speeds, feeds and depth of cut on a hobby mill and then fine-tune these parameters to suit your machine.

Sorry, Dale, I know this isn't the answer you want but it is the reality.
 

Jubil

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What mill do you have? My Bridgeport has a rheostat but has ipm graduations, although they are approximate. I usually start low and increase speed according to sound, and finish.
Post a pic of your power feed and some one on here probably has one with a label. They might post a pic to give you an idea where to start.

Chuck
Sorry, Mikey posted while I was typing. I may be misunderstanding the question.
 

Chewy

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Try this. There are charts all over the place with different speeds and feeds. The people on this forum are all over the place on feeds and speeds due to the individual machines and how rigid/powerful.
1018 steel is about 100 SFM x 4 divided by cutter diameter. So 1/2 HSS end mill is about 800 RPM and 5/8" is about 600 RPM. With 1/2" endmill set at 800 RPM touch off and go .015 DOC on steel. Slowly start increasing the X feed rate while watching and listening. 1. if the machine starts vibrating reduce speed until right at edge and then 2-3 percent below that. 2. If the chips start turning dark color, slow down feed rate. The chips should be bright and curly cued. Light blue is to be watched, dark blue to black is costing you money.

If you make it all the way across and it looks good, increase DOC to .020 and try again. Maybe increase RPM by 50 and try again. Maybe decrease by 50 RPM. The only way to figure out feed and speed rate FOR YOU is to sit there and cut metal for a couple of hours. Soon you will learn what is best for your machine. When I use carbide end mills I jack up the speed a couple of hundred RPM. Also if you buy used endmills from Ebay, they will not be sharp and that will throw you off on the calculations. By a brand new 3/8" or 1/2" 4 flute end mill and try it against one that you have and see the difference. Also, unless you have a 2000 lb. Bridgeport or clone, you will not be able to cut like the You Tube guys. Almost all of cutter speed, DOC, IPM and material information is set for professional machines, not HF specials.

If you took all of a popular machine like the PM 25 that the readers here have and lined them all up, everyone would cut at a different speed and feed rate. Rule of thumb; If the machine is happy, I'm happy!!!

Charles
 

rzw0wr

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I found a formula on RPM I will use.

SFPM X 4 / Cutter Dia. Ball part start RPM. I have only 6 speeds.

Then I found a SFPM chart.

Working OK for me.

Thanks for the tips and replies.

Dale
 
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