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Author Topic: Rule of Thumb.  (Read 11805 times)

Offline Stilldrillin

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Rule of Thumb.
« on: January 14, 2009, 04:11:46 AM »

Boggy`s posting & pics re.Darren`s lathe, took me straight back to my 36yr milling career, finished 3yrs ago.....

It surprised me to see the side & face cutter running at 200rpm........ :bugeye:
Until I realised it wasn`t my imagined 4” or 6” dia cutter! Probably only 1 1/2”.  :thumbup:

This set me thinking of my Rule of Thumb, which I`ve carried in my head for more years than I care to remember......

Based on 1/2” diameter = .500” = 500rpm.

Half that dia = twice the rpm.

Twice that dia = half the rpm.


RPM for drills & milling cutters, machining steel, with coolant.

1/16" = 4,000rpm

1/8” = 2,000rpm

1/4” = 1,000 rpm

1/2” = 500rpm

1” = 250rpm

2” = 125rpm

4” = 65rpm

6” = 50rpm

Proportionate rpm for inbetween sizes.

It still works!  :thumbup:
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David.

Still drilling holes... Sometimes, in the right place!

Still modifying bits of metal... Occasionally, making an improvement!

bogstandard

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Re: Rule of Thumb.
« Reply #1 on: January 14, 2009, 05:21:51 AM »
Dave,

In fact, that cutter was 3" diam., so by your calcs should run at around 90RPM (using steel).

Rules of thumb are great, and a very good starting point.

I listen and look at what the machine does with the material I am cutting, and adjust accordingly. My observations suggested that I could easily have increased the speed of the cutter by about 50% (300RPM) and doubled the feed (1/2" per min to 1" per min). That was just for this job, other materials may require reducing your rule of thumb settings.

So as you say, rules of thumb work, but as you well know, the material, type of cutter and machine will tell you when you have got it spot on.

John
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Offline Stilldrillin

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Re: Rule of Thumb.
« Reply #2 on: January 14, 2009, 12:14:32 PM »
John, a lot of my work included milling splines.

After several batches of these, you find the optimum speed & feed for the material......  :thumbup:



Then, on the next batch, the material changes......  :scratch:

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David.

Still drilling holes... Sometimes, in the right place!

Still modifying bits of metal... Occasionally, making an improvement!

Offline Bernd

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Re: Rule of Thumb.
« Reply #3 on: January 14, 2009, 01:04:10 PM »
Ok Dave,

What the heck am I looking at. At first I thought somebody had forgot to clean all the chips (swarf) of the part. Then I noticed numbers and what appears to be the beginings of holes. :scratch:

Oh ,and very big, by the looks of it, well at least quite heavy.

Bernd
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bogstandard

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Re: Rule of Thumb.
« Reply #4 on: January 14, 2009, 01:23:39 PM »
SD,

That looks to me like some sort of geological drilling head, minus it's tips.

You haven't got one knocking about anywhere? I need a bit of material for a new project. You pay the postage.


Bogs
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Offline SPiN Racing

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Re: Rule of Thumb.
« Reply #5 on: January 15, 2009, 12:15:23 AM »
Ohhh nice.
Im printing that rule of thumb out on 11x17 paper here at work and sticking it on the wall over my lathe next to the Tap and drill chart/poster.


Thanks!
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Offline Stilldrillin

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Re: Rule of Thumb.
« Reply #6 on: January 15, 2009, 12:50:49 PM »
Quote from: Bernd on January 14, 2009, 01:04:10 PM
Ok Dave,

What the heck am I looking at. At first I thought somebody had forgot to clean all the chips (swarf) of the part. Then I noticed numbers and what appears to be the beginings of holes. :scratch:

Oh ,and very big, by the looks of it, well at least quite heavy.

Bernd


Bernd, as know it all Boggy says, it`s a rock bit. Minus it`s carbide inserts....
Oh look..... Here`s another!



The numbers are gradings by the inspection dept.
Dependant on size of bit, nominal sizes 10, 12, 14, 16, 18, 20, 22mm. Each size with 5 available grades (coloured), in 5 micron increments.
The holes were drilled to an accuracy of 3 micron........ Mostly!  ::)

The bit was then heated and the buttons driven in.

I really showed that pic for the splining, with side & face cutter.

You might like to see the sort of thing we machined...... From solid......

Overburden drilling parts.







Funny...... I don`t miss working at all.....  :clap:
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David.

Still drilling holes... Sometimes, in the right place!

Still modifying bits of metal... Occasionally, making an improvement!

Offline Bernd

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Re: Rule of Thumb.
« Reply #7 on: January 15, 2009, 01:05:19 PM »
Thanks Dave.

That was very interesting and educational.

Drill bits to drill holes in the earth. Imagine that. :) Like for gas wells and such right?

Bernd
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Offline Stilldrillin

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Re: Rule of Thumb.
« Reply #8 on: January 15, 2009, 01:14:26 PM »
And many other applications Bernd.

Can`t dig a trench across an airfield runway.
Drill a horizontal hole under it instead........ :headbang:

Holes in Scandinavian permafrost, for telegraph poles......  :clap:

etc, etc........  :thumbup:
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David.

Still drilling holes... Sometimes, in the right place!

Still modifying bits of metal... Occasionally, making an improvement!

Offline sbwhart

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Re: Rule of Thumb.
« Reply #9 on: January 15, 2009, 02:01:16 PM »
Nice to see a good bit of heavy  :headbang: engineering


Cheers
 :wave:
Stew
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Offline Mjay

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Re: Rule of Thumb.
« Reply #10 on: January 16, 2009, 12:04:26 AM »
Now does that speed rule of thumb used for hss , carbide or both?

I enjoyed the pics  :beer:
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Offline Stilldrillin

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Re: Rule of Thumb.
« Reply #11 on: January 16, 2009, 02:10:45 AM »
Quote from: Mjay on January 16, 2009, 12:04:26 AM
Now does that speed rule of thumb used for hss , carbide or both?

I enjoyed the pics  :beer:

Thanks Stew, & Mjay!

The rule of thumb is for HSS drills, cutting quality engineering steels.
Faster, or slower to suit conditions......

Carbide drills, up to 25mm., I ran approx twice those rpm.

Carbide cutters...... I ran 50mm. at 900 -  1,000rpm. Pro rata for other sizes........


I`ve just remembered.  :scratch:
That second rock bit, with the inserts.......

We were supplying a driller who was contracted to drill 4,000 holes...... In Hong Kong.

Wondered if he was trying to sink the island.......
« Last Edit: January 16, 2009, 02:22:21 AM by Stilldrillin »
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David.

Still drilling holes... Sometimes, in the right place!

Still modifying bits of metal... Occasionally, making an improvement!

Offline HS93

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Re: Rule of Thumb.
« Reply #12 on: January 16, 2009, 02:35:27 AM »
How about a RPM for drills & milling cutters, machining brass alloy, I know i woul appreatiate one .

Peter
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bogstandard

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Re: Rule of Thumb.
« Reply #13 on: January 16, 2009, 03:29:50 AM »
Peter,

I don't want to step on Dave's toes, but I think you are asking 'how long is a piece of string' with that one, and almost no-one could keep that much info brainstored, as there are too many variables.

So here is a quickie link that gives a short explanation of a few of the variables and answers most of your question.

http://maelabs.ucsd.edu/mae_ms/feeds_speeds.html

But if you want to do a bit more research on it, type in 'machine feeds and speeds' into your favourite search engine.
In fact over the years, I have seen a lot of charts that can be downloaded or screengrabbed, then just get them printed up and laminated and keep them handy in your shop.

A lot of it is really down to experience plus a bit of trial and error.

Hope this helps.

John
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Offline Stilldrillin

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Re: Rule of Thumb.
« Reply #14 on: January 16, 2009, 03:33:00 AM »
Spot on, John!  :clap:

Thank you  :thumbup:
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David.

Still drilling holes... Sometimes, in the right place!

Still modifying bits of metal... Occasionally, making an improvement!

Offline websterz

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Re: Rule of Thumb.
« Reply #15 on: March 05, 2009, 08:12:30 AM »
Quote from: bogstandard on January 16, 2009, 03:29:50 AM
Peter,

I don't want to step on Dave's toes, but I think you are asking 'how long is a piece of string' with that one, and almost no-one could keep that much info brainstored, as there are too many variables.

So here is a quickie link that gives a short explanation of a few of the variables and answers most of your question.

http://maelabs.ucsd.edu/mae_ms/feeds_speeds.html

But if you want to do a bit more research on it, type in 'machine feeds and speeds' into your favourite search engine.
In fact over the years, I have seen a lot of charts that can be downloaded or screengrabbed, then just get them printed up and laminated and keep them handy in your shop.

A lot of it is really down to experience plus a bit of trial and error.

Hope this helps.

John

Twice as long as half of it...another good rule of thumb.  :med:
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