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Old 08-30-2007, 11:36 PM   #1
noodelz
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Default TECH Machining principles

I wrote these in response to an earlier thread but I thought I resurrect them for tech week.

Well here we go, here are some basic machining principles. First of all the whole basis of machining is Speeds and Feeds. Speeds meaning how fast you are spinning the piece of material in a lathe, how fast you are spinning your cutting tool in a mill, or how fast you are spinning a drill when makin hole. Feeds refers to how fast you are moving your cutting tool across the material you are cutting on a lathe, mill or how fast you are moving a drill bit into a piece. Now there are formulas for getting you in the rough ballpark but as far as I’m concerned, that’s school shit and doesn’t usually ever apply to real life situations.

Now there are many different variations of speeds and feeds depending on the type of material you are machining and what type and shape of cutting tool or insert you are using. Some different types of cutting tools are Highspeed steel (more of the old school of machining, very cheap, you can grind different shapes depending on the job, but edge does not last very long, I still use them for certain specialty jobs), brazed on Carbide (where there is a piece of carbide brazed onto a piece of high speed steel, it has the toughness of a carbide insert and the versatility of Highspeed steel because you can grind different radius‘s, and shapes), carbide inserts (have different shapes depending on the use, and are coated with a thin layer of carbide. A good all around choice because they have multiple cutting edges so they can be indexed when an edge wears out, and cheaper to replace then CBN, Ceramic, and Diamond)), Ceramic (Very hard and brittle, good for cutting very hard materials, 50-65 Rockwell), Cubit Boron Nitride affectionalty known as CBN cause the full name is too hard to remember cause come on, we’re Tadesman not Chemists! (also good for cutting harder materials, not used too often, because of price), and Diamond (need I say more?, Extremely hard, good for hard materials, lasts long, but very expensive, I myself have never machined with diamond but I would love to sometime).

There are many different types of materials that can be machined, everything from urethane to IHCP (Induction Hardened Chrome). Different materials machine as different as their name, from the type of chip that is created to the type of finish that is made. For example 1020 (Mild steel) is very soft (about 4-5 Rockwell) so it machines more like gum, and does not normally leave a nice shiny finish without polishing. Whereas 4140 for example is harder (approx 24-28 Rockwell) machines very nice and leaves a very shiny finish at very high speeds for a finishing cut. IHCP (Induction Hardened Chrome) has a layer of hardened chrome for about the first approx .125” per side, so ceramic is definitely suggested for machining, until that layer is removed because the material under is kind of like a cross between stainless steel (gummy) and 4140, so it will wear out your ceramic. Carbide is recommended in this situation. I could go on and on about cutting tools vs. materials but for those of you that haven’t clicked the back button or fallen asleep by now will if I keep on rambling on about these.

Now you’ve heard me mention “finish”, that refers to the looks and smoothness of the material when you are done machining it, also called “lay“ (the closer the groove that your tool causes on the piece the smoother the finish. Even mirror finishes have microscopic grooves across the piece caused by the tool nose, they are just so fine you can‘t see them with the human eye). When you are machining and running your speeds and feeds on a lathe for example, the material is spinning at a certain rpm and the cutter is moving across it at a certain rate set by the machinist. For example if you have a lot of excess material to remove, you rough it off which means you remove as much as you can, as fast as possible (if you worked in a shop and were on a time limit you would know about “as fast as possible“). So in this case you don’t care about the finish because that will come later. Figure out how fast you should spin your material (bigger=slower, smaller=faster) and I like to set my feed rate at around .015-.020, this means that the cutting tool moves .020” across the piece per revolution of the piece. This is a good fast feed rate for roughing because it removes material fast (and throws nice hot chips so watch out). Next for finishing and sizing I like to leave about 0.030” to size properly, set my feedrate slower and depending on the material bump my speed up. Now you don’t want to set your feedrate too slow and have the tool drag across the material because it will mess up your finish. So with my machine set up and the piece cooled off to room temperature (cause we all know heat causes expansion of metal which will give you an inaccurate measurement), I come in about .020” and start my cut, I stop it about a ½” in and pullback. Now depending on the tolerance (the biggest or smallest size that a finished piece can be which is dictated by the application of the piece itself) of the piece being made, I will take a measurment with either my Mics (if it‘s a close tolerence,+/- .0001-0.001“), or my caliper (+/- 0.0002 and bigger). Now you know close to what depth of cut your machine is actually taking because any deflection from taking deep heavy cuts is gone and the precision kicks in. So in a perfect world my measurement would tell me to take another 0.010” to bring me right to size. But as we all know, machines get worn and we have to compensate so I usually stay 0.0005” away because you can always emery off the rest if you need to. I take my finish cut and call her good.

I’m gonna wrap this up for now cause I’m goin crosseyed looking at the screen. Now I have only scratched the surface (excuse the pun) of machining processes and tools. Everything I’m talking about pertains to Manual Machining where you use your own brain, skills and experience. Here in the 21st century we have CNC (Computer Numerical Control) Machining where there is a program written and the computer does alot of the work. It has it’s uses in production but as far as I’m concerned I don’t want to ever have anything to do with it.

Hopefully you were able to decipher my jargon and learned a little something along the way. NOW WAKE UP I’m DONE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!For now….
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You know (these days), looking cool when parked has a much higher priority that actual useful function.

YOU NEED TO CHECK THIS OUT! I'M STRONGLY SUGGESTING IT! YOU'LL BE GLAD YOU DID....
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Old 08-30-2007, 11:39 PM   #2
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Default Re: TECH Machining principles

And for some Milling stuff

Was milling some pieces at work today and started to think of some notes to post tonight....

One of the things with milling you really have to be careful of, is which way you cut from. There is one way where that is called "Conventional" Milling where the piece moves into the tooth of the cutter. And the second is called "Climb" Milling where the piece is moving in the same direction as the tooth of the cutter is spinning. It almost looks like it is rubbing the chips off and not actually cutting. This can be a dangerous process because the cutter wants to tend to climb up on the piece and spit it out hence the name "Climb". When milling like this I recommend a very ridgid set-up, and a backlash eliminator because the cutter is in a sense pushing the piece along and might make the whole mill Jump and spit the piece out at you. Sorry, "Backlash" is the play between the gears in the mill, the crosslide moves on a lead screw (a long shaft with an Acme thread on it), and a nut with the same internal thread. There is slop between between the fit of both the shaft and the nut, this is called "backlash". These nuts are usually made from brass so they tend to wear out after time which increases your backlash. Anyway, long story short, climb milling takes impact pressure off your cutter and really is usually only used for the nice finish it leaves. So I would recommend milling conventional to be safe. Also if you are using a face mill, and your piece is narrower than the diameter of the cutter, set it up so the cutter is staggered to the piece on the Conventional side (where the tooth spins and runs into the piece).

When machining with an End Mill and plunging into the piece to make slots for example, climb milling doesn't come into effect because the cutter is in the piece so it climbs and conventional mills. This also gives the piece a little more stability with the cutter in the piece because it is gives a more even chip load per tooth on the cutter to keep it from jumping.

All in all, the ,most important thing I can stress is have as RIDGID of a setup as possible, just in case you do start to climb mill without knowing. This way you won't be dodging flying schrapnel....

Oh I forgot, make sure to flood your coolant if you are using a High Speed Steel cutter, cause it won't last long if you don't.

Here's a couple pics, you'll have to excuse the crude artwork, my paint skills aren't exactly up to snuff....but you get the idea....





My buddy had one of those benchtop 3 in ones. It was good for small things, but the chatter because of not being a very ridgid setup was bad. You really had to play with your speeds, feeds and depth of cut. They's perfect for the hobbyist who make the odd things here and there, things where the tolerences aren't very tight. If it wasn't for me being lucky and havin first dibs on the old equipment from the shop (because I'm the one who decides when it's time to replace it lol) I would be usin one of them because of the price and convienence.
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You know (these days), looking cool when parked has a much higher priority that actual useful function.

YOU NEED TO CHECK THIS OUT! I'M STRONGLY SUGGESTING IT! YOU'LL BE GLAD YOU DID....
http://lowsidemag.blogspot.com/
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Old 08-30-2007, 11:48 PM   #3
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Default Re: TECH Machining principles

Good info. I'm still learning how to run my lathe, next is a mill.

Thanks.
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Old 09-01-2007, 02:42 AM   #4
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Default Re: TECH Machining principles

Killer post! Keep adding, I tried to get the local Votech to do a community ed class on this to no luck!
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Old 09-09-2007, 12:13 AM   #5
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Bttt
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Old 09-09-2007, 07:42 AM   #6
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Default Re: TECH Machining principles

this is great stuff. i also just got a pair of books from amazon that are excellent.

http://www.amazon.com/Machine-shop-P...9337796&sr=8-1

and

http://www.amazon.com/Machine-Shop-P...9337796&sr=8-2

i will also be looking into the franklin jones books as well. they are cheaper than most paperbacks and jammed with info. they are dated, but these are principles that haven't changed in decades. the info is so abundant it's overwhelming, and there's lots of info that you probably won't need like turret lathes, radial drill presses and jig borers. hell, even if you don't plan on machining so much as just hacking out brackets with a grinder and a drill press, the info on layout and drilling is invaluable.

the only problem i have with these books is they make me want to buy lots of heavy equipment and expensive tooling!
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Old 09-09-2007, 10:31 AM   #7
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Default Re: TECH Machining principles

Excellent tech write up Noodlez........
Heres a helpful link I'll toss in
http://www.jjjtrain.com/vms/
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Old 09-09-2007, 10:36 AM   #8
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Default Re: TECH Machining principles

good reading with my morning cup of coffee...thanks Blair!
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Old 09-09-2007, 11:39 AM   #9
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Default Re: TECH Machining principles

Machinery's hand book is worth its weight in gold, check it out.

http://www.use-enco.com/CGI/INSRIT?P...PMPXNO=8253092
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Old 09-09-2007, 10:42 PM   #10
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Originally Posted by Rojo View Post
Machinery's hand book is worth its weight in gold, check it out.

http://www.use-enco.com/CGI/INSRIT?P...PMPXNO=8253092

Thanks guys, I'm gonna be in a cast for 3 months I just found out cause they have to put a screw and a bone graft in my right hand. So that will give me more time to write more up, the more knowledge people have starting something new the better. Knowledge cuts down on costs, accidents, and time, I'm happy to share mine when people are intrested, I've been doing this for alot of years and have seen what works and what doesn't, don't get me wrong I still learn everyday which is the cool thing about the trade. As technology grows with CNC's and shit old school manual machinists like myself grow scarce. But as fast as they are, head to head I can still beat any of our machines for a one off.


The Machinery's Handbook is good but there's ALOT of info that is not really needed unless you're writing a Metallurgy/Machining/lot's of stuff a guy will not ever use Thesus or somethin. The book to pic up is the Machinery's Handbook Quick Reference. It's about 1/8th of the pages and it's got all the important info like Tap Drill Size, thread forms/formulas, some metallurgy, etc. I'll try and find a link for it, and it's less than half the price of the regular handbook.
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Just get out there and (buy bike, ride bike, re-engineer bike in garage etc..)
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Originally Posted by Dragon View Post

You know (these days), looking cool when parked has a much higher priority that actual useful function.

YOU NEED TO CHECK THIS OUT! I'M STRONGLY SUGGESTING IT! YOU'LL BE GLAD YOU DID....
http://lowsidemag.blogspot.com/

Last edited by noodelz; 09-09-2007 at 10:50 PM.
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Old 09-09-2007, 11:10 PM   #11
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Default Re: TECH Machining principles

Noodelz,

Awsome stuff man. Thanks for posting. This stuff is invaluable knowledge. I've started reading a couple basic princple books and trying to learn as much as posible about this. Something I've always wanted to learn. Unfortunatly, I don't have the means to take classes right now. So I'm looking to pick up a hobbyist mill to practice with. Please keep posting more as you get a chance. Great stuff.
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Old 09-10-2007, 07:20 AM   #12
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Default Re: TECH Machining principles

Good info.

Also, it's easier to take metal off than put it back on if take too heavy of a cut.

And the telltale chip, which means watch your chips they'll tell you if your cutting too hot, too deep, not deep enough, too fast/slow...etc.

I would recommend a 12" SS Starrett single hook scale for a manual machinist. The most useful tool you'll have, it could be used as a chip hook, back scratcher, screwdriver, dull knife, scraper and a measuring instrument.

Last edited by Spiderman; 09-10-2007 at 07:39 AM.
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Old 09-10-2007, 09:18 AM   #13
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Default Re: TECH Machining principles

I inherited my grandfather's machine shop books from WWII - what a great resource.

For you guys looking for books, try your local used book stores. There's one down the road from me that has an entire wall of old machine shop books and engineering books from the early 20th century up. It's a great way to get some old school (for real) knowledge on the cheap.
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Old 09-10-2007, 11:37 AM   #14
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I inherited my grandfather's machine shop books from WWII - what a great resource.

For you guys looking for books, try your local used book stores. There's one down the road from me that has an entire wall of old machine shop books and engineering books from the early 20th century up. It's a great way to get some old school (for real) knowledge on the cheap.
Thanks for the tip!
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Old 09-10-2007, 03:38 PM   #15
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Good info.

Also, it's easier to take metal off than put it back on if take too heavy of a cut.

And the telltale chip, which means watch your chips they'll tell you if your cutting too hot, too deep, not deep enough, too fast/slow...etc.

That's right, chips tell all. Once you get used to it you can find the right speeds and feeds by just watching the way the chips come off the piece. It's funny back in the day making one continuous long stringer chip was considered the best, but now with the new tech inserts with chip breakers and shit the chips are optimal when they look like 6's and 9's for roughing. But still a fairly one piece chip for finishing because of the light cut.
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Dragon

The problem stems from relying on internet opinions to frame your perspective and actions.


Just get out there and (buy bike, ride bike, re-engineer bike in garage etc..)
just DO IT.
Quote:
Originally Posted by Dragon View Post

You know (these days), looking cool when parked has a much higher priority that actual useful function.

YOU NEED TO CHECK THIS OUT! I'M STRONGLY SUGGESTING IT! YOU'LL BE GLAD YOU DID....
http://lowsidemag.blogspot.com/
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Old 09-11-2007, 09:00 PM   #16
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Worthy of the Tech section
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Old 09-11-2007, 09:31 PM   #17
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Worthy of the Tech section

Cool man thanks. Will get on the go prolly next week on some more.
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The problem stems from relying on internet opinions to frame your perspective and actions.


Just get out there and (buy bike, ride bike, re-engineer bike in garage etc..)
just DO IT.
Quote:
Originally Posted by Dragon View Post

You know (these days), looking cool when parked has a much higher priority that actual useful function.

YOU NEED TO CHECK THIS OUT! I'M STRONGLY SUGGESTING IT! YOU'LL BE GLAD YOU DID....
http://lowsidemag.blogspot.com/
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