Drilling and milling questions

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mikechoochoo
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Drilling and milling questions

Post by mikechoochoo » Thu Jan 24, 2019 10:22 am

I was wondering, when drilling a large hole in mild steel given a 1/2 hp motor and drilling in steps, how much material should you remove in each step? I'm thinking of holes over one inch. This is just in my home shop for myself so I'm not worried about time. Also what is the largest hole I could drill in one step?

Second, in milling with end mills under 1/2 inch, are there tables or a formula that show what the safe depth of cut is for different sizes of end mills and different materials? Again I'm not worried about speed, but more about the life of the endmill.
Thanks,
Mike

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SteveM
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Re: Drilling and milling questions

Post by SteveM » Thu Jan 24, 2019 1:41 pm

If you are drilling large thru holes, consider a slug cutter - it's like a hole saw on steroids (not good for blind holes).

On my lathe (1/2 hp), I will drill 1/4", then 1/2" (maybe an intermediate step in steel), and go up in 1/8" or 1/4" increments from there.

The lathe is nice because I can get a much slower speed than the drill press (until I get the slow speed attachment installed).

Steve

earlgo
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Re: Drilling and milling questions

Post by earlgo » Thu Jan 24, 2019 3:37 pm

Speeds and feeds is a relatively complicated subject depending on your understanding of machine tools, materials doing the cutting and materials being cut.
For a start you might want to look athttps://www.whitneytool.com/SpeedAndFeedCalculator.aspx.
You also might want to find a copy of South Bend's " How to Run a Lathe". A .pdf of an older version can be found here:
http://www.vintagemachinery.org/pubs/1617/3789.pdf
Or you might find one on Amazon or at a local book sale or second hand store or a flea market.
--earlgo
Before you do anything, you must do something else first. - Washington's principle.

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rudd
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Re: Drilling and milling questions

Post by rudd » Fri Jan 25, 2019 7:40 pm

For feeds and speeds, I typically use Little Machine Shop's calculator.
They have cutting speeds listed on one page, https://littlemachineshop.com/reference ... speeds.php
and a calculator nearby.
https://littlemachineshop.com/mobile/speeds_feeds.php

I see now they have updated the calculator to automatically input recommended cutting speeds (based on using HSS) for each material in the calculator itself, but you can adjust them. I double for carbide and half for carbon steel. It will even take an input for a 6" diameter horizontal mill cutter.
As far as depth of cut for endmills, I've heard 1/2 a diameter as a starting point. I don't use them much.

EOsteam
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Re: Drilling and milling questions

Post by EOsteam » Sat Jan 26, 2019 3:29 am

On the Little Machine Shop page it lists under the “turning” section a range of ft/min for most materials. For instance under “Plain Carbon Steels” the range is from 125 - 215 ft/min for HSS. How does one know what value to use inside the range for a particular material? 1018 vs.1025?
What about the wrought Aluminums?
Thanks.
HJ

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SteveHGraham
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Re: Drilling and milling questions

Post by SteveHGraham » Sat Jan 26, 2019 9:34 am

If you're drilling relatively thin material, a step drill is a wonderful time-saver. It will turn a 3/32" hole into a 1/2" hole in no time.
Every hard-fried egg began life sunny-side up.

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rudd
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Re: Drilling and milling questions

Post by rudd » Sat Jan 26, 2019 2:05 pm

I use those numbers as a starting point. But they do give a *range*, so you can hit somewhere in that range to suit your fancy. On lathe work I tend to use the upper range (only cost of burning a cutter is a moment at the grinder), on the mills I usually aim for the lower end of the range (milling cutters are expensive). The do give different figures for 1025 v 1019 on the chart (first link). Worthwhile to note for example that 100fpm is well inside the range for both.
They also list wrought aluminum, v. cast aluminum.

pete
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Re: Drilling and milling questions

Post by pete » Sat Jan 26, 2019 6:49 pm

Almost impossible to answer with any certainty about the maximum hole size. It all depends on the machines design and rigidity. As an example, a 250 lb 1/2 hp bench top drill press couldn't drill holes with any 1/2" or larger drill half way as well as a 1/2 hp 250 lb bench top lathe could. The difference is all about how well the work and drill is held and supported. I've seen YT videos showing little Atlas horizontal mills taking depths of cut my 3 hp Bridgeport clone might struggle with. My available hp isn't the limit, how flexible a Bridgeports design is and how rigidly the cutting tool is supported is then the problem. The old school formula in reference manuals like Machinery's Handbook for HSS is 100 ft per min in mild steel and 1 cubic inch of material removed per minute per hp. Those would be industrial numbers calculated for heavy duty rigid machines and they assume flood coolant is being used. Depending on the machines rigidity and the low end torque available I suspect anything over 1/2" in diameter will take lot's of patience. Vibration caused chatter can kill or chip the cutting edges far more than the cutting action at that point. Core type drills or single point boring might be the better option then.

End milling? Depending on the material and machine I'll usually figure on 1/3rd - 1/2 the end mills diameter for depth of cut as a good rough starting point. For any end mill and especially under 1/2" a consistent feed rate is as important as the depth. Too little and the tool rubs and quickly wears out, a bit too much and you have a two piece cutting tool. :-) Even chip re-cutting has a serious effect on tool life and breakage. Those recommended feed rates are all about the chip load per tooth and the machines rigidity. Again exact cutting tool parameters will depend a great deal on what the machine itself is capable of and the material your cutting. For light weight hobby level machines I doubt anyone here or any chart available can give 100% reliable numbers without someone having multiple hrs operating the exact same machine that can say for sure what will work. I've got some seriously work hardened scrap bronze plate here that doesn't like any numbers for any bronze alloy that I've found online so it's more about starting a bit low and working up until the machine tells you it's enough. For that bronze using the speeds and feed numbers for 304 stainless seems to work about as good as anything else I've tried. I've yet to figure out how to gain that experience without burning up or breaking a few end mills though.

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rudd
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Re: Drilling and milling questions

Post by rudd » Sat Jan 26, 2019 9:24 pm

Pete is spot on. One thing I will comment on:

"I've seen YT videos showing little Atlas horizontal mills taking depths of cut my 3 hp Bridgeport clone might struggle with"
I was told the way to set the feed on a horizontal is to keep increasing it till the machine starts jumping around on the floor, then back off a little. My horizontal is currently, and usually is, at some odd angle in relation to the wall behind it.

pete
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Re: Drilling and milling questions

Post by pete » Sun Jan 27, 2019 1:49 am

Yep it's pretty amazing what supporting a cutting tool at both ends can accomplish verses having only one end in a collet on a vertical mill Rudd. Your method sounds about right though. :-)

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