### Author Topic: material/rpm chart print out for VFD drill press?  (Read 1176 times)

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#### coppercone2

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##### Re: material/rpm chart print out for VFD drill press?
« Reply #2 on: April 10, 2022, 06:13:33 pm »
Yeah I would need to verify how VFD setting adapts to drill. Is there a sensor that I could put a small magnet on the chuck or something and use a sensor to discipline RPM?

#### mc172

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##### Re: material/rpm chart print out for VFD drill press?
« Reply #3 on: April 10, 2022, 06:31:24 pm »
Why is the spindle speed so important to you? It's not that critical.

I just calculate it each time and because I've done it so many times I've remembered certain cutting speeds for a handful of common materials. You only really need to remember three or four - steel, stainless, aluminium and maybe brass.

The formula is easy, it's the cutting speed in mm/min divided by the circumference of the moving part. The output is in RPM.
A working example: drilling a 10mm hole into stainless steel.
Cutting speed approx. 30 m/min = 30,000 mm/min.
Drill diameter = 10 mm
Speed = 955 RPM

But remember this is a maximum and you don't need to get the spindle anally close to that speed. Half that speed will still do the job.
You will also get an intuitive feel for it as time goes on. You won't need to calculate it each time as you'll get a feel for where the ballpark is.
With small diameter drill bits in soft metals like brass and aluminium, the equation will output speeds that you won't be able to achieve, like 10k RPM. Just run as fast as you can. If your pillar drill makes a racket at that speed, which it probably will, it's fine to go even slower than that.

Regarding rake angle and all that, just use good quality general purpose HSS drill bits like Dormer or Guehring. It doesn't need to be that complicated. It's totally impractical unless you're in a production enviroment to stock all those different grinds and absolutely bonkers if you're considering regrinding drills on a per material basis.
« Last Edit: April 10, 2022, 09:12:40 pm by mc172 »

#### TimFox

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##### Re: material/rpm chart print out for VFD drill press?
« Reply #4 on: April 10, 2022, 06:31:50 pm »
With "regular" drill presses (multiple pulley diameters), the drill speed charts (simple or complicated) always refer to the rpms at the chuck, usually specifying the discrete set of rpms with four or more configurations of the drive belt on the pulleys.  I assume your VFD drive has a fixed ratio from motor rpm to chuck rpm.
For "really big" charts of cutting speed, you probably want a copy of the "Machinery's Handbook".  A free pdf of the 29th edition is at  https://engineeringbookspdf.com/machinerys-handbook-29th-edition-pdf-free-download/5424/
##### Re: material/rpm chart print out for VFD drill press?
« Reply #8 on: April 10, 2022, 10:29:19 pm »
Well, I was never sure how big this table would be, that's why I was kinda hoping that someone had something that was generalized to manual drilling machines with variable speed control, based on typical operator performance or something. (there are some really fancy drill presses out there, I thought maybe some manufacturer had made this kind of table or it was a popular standard of some kind.

That's why I thought the existing information that I am aware of is not going to be useful because of the down pressure element. But I thought maybe someone knew about a manufacturer that happened to have a chart or something because they did some kind of large scale research on a population group to have 'general' settings that are a good point to start for a manual operator....

Like what I am saying maybe some one saw an attempt by a manufacturer to provide this information.. like I know you have some drill press that have continuously adjustable RPM rather then the typical belts on pullies, they might have bothered to try to dial in some specific numbers along a best fit line or something.
« Last Edit: April 10, 2022, 10:35:00 pm by coppercone2 »

#### Domagoj T

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##### Re: material/rpm chart print out for VFD drill press?
« Reply #9 on: April 11, 2022, 02:01:17 pm »
This seems reasonable, it assumes usage of HSS drill bits (I wouldn't use carbide on a drill press unless it's very rigid and has good workholding, other than for PCBs which are very abrasive and will eat away the HSS):
https://wiki.ideashop.iit.edu/images/f/f7/DrillPressRPMs.png

It lacks data for stainless, but you can eyeball it to about 20% - 40% of steel data.
jpanhalt raised a good point. There are different alloys of the "same" material that behave very differently. Most stainless steel alloys like to work harden and going slow (slow feed) will not work. You must be a bit aggressive and not allow the bit to rub because that will produce a very hard surface that you'll have trouble penetrating later on. Also dull bits are just not gonna cut it.

This chart is more aimed at CNC machining but might also help you.
Keep in mind that "Speed SFM" is not RPM, it's surface speed in feet per minute, aka cutting speed.

All this being said, VFD is nice and all, but if you plan on drilling a lot of big holes in steel, it might be better to keep the belt and pulley system since it provides the torque at low RPM, which VFD might struggle with.

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#### Gregg

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##### Re: material/rpm chart print out for VFD drill press?
« Reply #10 on: April 11, 2022, 08:32:57 pm »
Get a copy of Machinery's Handbook; it has answers to everything you are asking.  They are readily available on ebay used and you don't need the latest edition.

#### jpanhalt

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##### Re: material/rpm chart print out for VFD drill press?
« Reply #11 on: April 11, 2022, 08:56:48 pm »
Get a copy of Machinery's Handbook; it has answers to everything you are asking.  They are readily available on ebay used and you don't need the latest edition.

Exactly.  I have 3 copies.  Two in paper form and one on CD.  I never look at the one on CD.  But, I designed a hangar door 18' high by 50' wide using one of the paper versions, and it has withstood almost 40 years of Minnesota thunderstorms.  Adjacent hangers have not been so lucky. (attached)

#### coppercone2

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##### Re: material/rpm chart print out for VFD drill press?
« Reply #17 on: April 12, 2022, 09:02:42 pm »
Is that pressure table in PSI? I see a scleroscope is some kind of hardness tester. Not sure if the units are whatever is used in a scleroscope?

And a normal point means like one that has a small flat on top?

#### BrokenYugo

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##### Re: material/rpm chart print out for VFD drill press?
« Reply #18 on: April 12, 2022, 09:35:44 pm »
I read that as downfeed pounds force, standard drill grind with the web in the middle, not split point.

Smf