Material and tool selection

[MeJasonT]

For ages now i have been trying to unearth the magic behind material and tool selection. The people with the knowledge protect it like the Holy Grail and it shouldn't be so hard to bust the myth.
The problem is two pronged:-
As a new starter,SME or hobbyist in machining you go to your local steel stockist and ask for some steel, obviously they come in different hardness's and machine abilities as well as Alu, brass, stainless etc.
I made the novice move of buying mild steel bar for a project and found i had a huge learning curve ahead of me. Incidentally Mild steel not good its gummy- ie it sticks to tools dose not evacuate well and generally sluggish to cut.

Now you would think my metal stockist would suggest materials that would be best to use, No he had no idea what i was talking about when i asked about machineability of various materials. I found a nice list of four digit codes for various materials in the US but this apparently did not translate to the BS (British standard he understood or EN). I spend my life on Google, i'm one of their best patrons - hasten to add hours of searching has been unfruitful.
I didn't go to college and learn to be a machinist, so i suspect my lack of knowledge lies there. I'm not sure if material science is even taught on machinist courses.

The same goes for Tooling, if i buy from Ebay, Cutwell - a tooling supplier or my local steel stockist i don't get any information on the tool.
chipload and radius angle seems to be two bits of information they don't share - kind of important one would think.
I have taken to looking at similar tools in other manufacturers tooling catalogues and working out what i have bought, its working OK for now but its pretty shoddy really. My question to you all is can we debunk the myth and finally put the speeds and feeds to bed for the inspired and knowledge thirsty beginners. I find KISS is the best method so if you are an aeronautical specialist perhaps your insight will be airborne above the heads of many.

After many years I have finally worked out how to source and size index able lathe tips which I previously had to go back to the lathe manufacturer for as their part number was not an industry standard one but their own convoluted number. This is the best site with the most knowledgeable people to hammer out this topic as the vast array of experience far outweighs the rather limited information we can get from suppliers of over protective professionals.

Looking forward to your replies.

[ncollar]

MeJasonT
Jason, I am a old school person and find a lot of my knowledge from U-Tube videos. I do not exactly understand what you mean about the metal you were trying to work with. One of the things I have learned is if it does not look good start playing with the speed and feed. Every metal has a magic point that will work rather well. I know this because a lot of my stock is repurposed material. I have collected things from an old auto like axles and springs. Very good metal but very hard. Good luck and success.
The best advice is go slower but for aluminium it is faster!
Nelson

[jmparker98223]

For ages now i have been trying to unearth the magic behind material and tool selection. The people with the knowledge protect it like the Holy Grail and it shouldn't be so hard to bust the myth.
The problem is two pronged:-
As a new starter,SME or hobbyist in machining you go to your local steel stockist and ask for some steel, obviously they come in different hardness's and machine abilities as well as Alu, brass, stainless etc....
SNIP!
Looking forward to your replies.

Look to the "Machinery's Handbook" published by Industrial Press Inc. New York ISBN 0-8311-1200-X for more information than most can use in a lifetime. You'll find cutting tool and relief angles, speeds and feed info on many materials therein. The real issue is identifying the material that you are trying to work with and the appropriate cutting fluid to suit. The wrong cutting fluid can make an easy job difficult or impossible.

Buy a secondhand edition to save a few bucks. Best wishes...

[PJs]

MeJasonT, well said and I feel a need for a simple chart or calculator also, but there are way too many variables to come up with the perfect speed and feed, imho. The basic formulas apply to turning, milling and drilling operations and there are calculators for that from cardboard wheels to AP's on your phone or tablet OR one of these. The real issue as you point out are the materials and Knowing what you are actually working with. Like ncollar said, Us home-shop guys pretty much scrounge "Mystery Materials" and you don't know till you take your first bite for how it's going to react, but can do such things as spark tests for carbon content, etc. The other issues are the machine itself, it's rigidity, hp, TIR, etc...and of course tooling, HSS, coated, Carbide, inserts (Types, rake, relief, radii, etc)...and their matching holders.

I'm a materials guy and Non Aeronautical engineer and I can say that the Materials field has mushroom clouded over the last 15-20 years with new ones every day. When I designed the drill machines I had to work with copper (hard), aluminum (extruded), Stainless (several varieties) and the occasional Inconel and Hastelloy. They had 4 drill heads and about 20 different type tools, including 2 sizes of rotabroaches necessary to do the operations. Basically I could get the speed and feed info because I knew the material properties and could choose a bit or tool within reason for the op, but they didn't work every time because of the machine and the Desouter Drills (Mighty fine British Product) I used on them, so it became a bit (unintended pun) of trial and error to get them right so the tools would last, not break and do the op to the tolerance I needed. Basically it became a 4 page B-size (11x17) spreadsheet you could barely read on paper for each drill, operation type, material, with a basic tool setup system (4 letter code). That took a month to ferret out and test.

Fast forward to my mini-lathe...it's still a process mainly because of "Mystery Material" and how the Mini handles it. One of the hardest things I turned on it was a piece of 2" G2 Grey bar (Cast iron) and I knew what the material was and roughly what speed I should turn it...just a bit much for the mini, but got through it. Even the brass I buy or scrounge up seem to react differently with each piece. 18/8 or 17-4 stainless on the other hand spins nice with a good finish but cold rolled (1018), isn't pretty, but 1144 stress relieved is a pleasure with slower feeds.

Here are a couple of links for perusal.

https://www.wisc-online.com/Learning...02/MLT8202.htm

https://littlemachineshop.com/refere...tingspeeds.php

https://www.onlinemetals.com/ They have some basic material information on each of the materials they carry.

And of course the Machinery's Handbook. Amazon or Ebay I'm Sure they are available in the UK.

Basically I have become to believe it is part magic and knowing your machines, tooling and materials. I've blathered on here and do hope Doug, TM51 or other wizards will chime in here as I think it's a good topic to run up the discussion tree for the noob's, wanna be's (like me) as well as others.

PJ

[hemmjo]

MeJasonT, The problem is as you mention in the first line of your post, it is all "magic", so it is difficult to find the real answers you want.

As others have mentioned there are just so many variables, any chart that you find in regard to the information you are seeking, just gets you close. As you continue to work with more and different metals from various sources, either purchased from a supplier or simply found along side the road, you will learn how the many variables affect the results of your machining efforts.

Make sure your machines are "tuned up" as good as you can get them. Loose spindle bearings, and slide gibs, and feed screws will make it difficult to get good results with even the perfect combination of cutting tool, material, speed and feed.

After getting my lathe tuned up, I have made the most progress focusing on how the cutting edge is presented to the work piece. I removed the "rocker" from my lanter type tool post and replaced that with flat steel disks of various thickness and thin strips of steel shim to adjust my tool height. This made my tool post much more rigid and does not change the cutting tool angles as the rocker did while adjusting tool height.

I have not had much luck with carbide. The number 1 reason is I cannot afford to have have enough different shapes and sizes for all of the various types of work I do on my lathe. I do not think 11" Logan lathe is rigid enough to use carbide effectively. I have learned however to sharpen High Speed Steel cutting tools effectively to produce some fine results on various materials.

Cutting edge geometry is a balance that changes, some times dramatically, according to material properties. Don't be afraid to experiment with clearance and rake angles, as well as surface finish of the tool itself as you experiment with machining various materials. If the angles are too severe, the edge becomes "sharper" but also much weaker, subject to breaking and and less able to carry heat away from the cutting edge. Too much rake can "pull" the tool into soft materials, to little rake can allow the chips to rub against the finished surface leaving it rough. If the surface of the tool is rough, with small ridges from the grinding wheel, the material you are removing can stick and weld itself to the cutting tool, leaving a rough finish. Depending on the finish requirement, I often "polish" the cutting edge on a hard stone after grinding to remove the grinding marks. I also keep a small hard stone at my lathe to touch up sometimes. So many variables here also.

Cutting fluids and lubrication also play a big roll in machining results. In my situation I am limited because my little shop is in my basement. I cannot use many of the available cutting products due to the smell. In the old days some used lard. I have found that "Crisco" in the paste form works well for things like taping, sometimes I use it for turning. When my wife comes home, she has said "what are you cooking" instead of, "EWWWWW what is that smell?". I also use Ballistol (google it) mixed with water, works well for turning and drilling.

There are just so many factors that affect your results. Some times very subtle changes in your set up make a big difference in results.

Good Luck,

John

[MeJasonT]

Thanks guys, its got the topic off to a good start.
The direction which I was hoping this post would go in was more of a mind dump of peoples knowledge, I appreciate the interest and feedback so far.

When I first started to machine with CNC I went down the youtube and machinists forum route but somehow the question keeps getting asked by novices and hobbyist's over and over again. Its really hard to say to those who are knowledgeable what you are trying to get your head around even though they must have been at the same starting point at some time. the calculations are all well and good but rarely coincide with those provided by the tool manufactures which tend to suggest much higher feeds and speeds. When you first enter the the art of machining you become overwhelmed by the amount of information and the contradictions of different sources. I agree there are a vast array of variable which need to be taken into account mainly about the machine and its idiosyncrasies. If for a moment to set that aside and state that the machine is sturdy, no loose mechanisms and sufficient torque - lets face it even big machine shops will find the limit of their machines eventually. When faced with the daunting task of running a machine for the first time, running the spindle at 10,000 RPM and cringing as the tool speeds its way towards the work piece scares the crap out of any normal red blooded person especially if it end in a ping or clunk. No quite as bad as a high pitched scream - crashed helicopters are far worse, that noise of an engine trying to spin a rotor through a seized gearbox, that noise never leaves you. Most newbies just want to avoid the initial pain especially if you have built, retro fitted or purchased a machine and using it for the first time.

CNC also has the gotcha of having its own brain to keep going whatever happens, thank the almighty for the big red button.

If we collate all the experimentation and material trials we do then hopefully we can find a common thread which can be used as a template.

Nelson,s reply giving me/us an insight to material he has worked with is insightful, I wasn't expecting not getting reamed for using mild steel. Bright steel bar seems to be the better choice but if there are some out there who can tell us what they usually order and machine with and a direction to tool, feeds and speeds used would hopefully provide us/newbies with a good starting reference.
(John) hemmjo & PJ fantastic info many thanks guys. jmparker, i've got the book, thanks for the suggestion.

Any commercial machinist who has a point of view of well its simple just use the formula etc. then you should reassure yourself that you may be responsible for injury or death of newbies, lets faced it theses things are killers they have teeth and everything. Its too late reducing the feed if you are wearing a 3/8th 3 flute HSS tool in your head, look on the bright side it didn't get you in the eyes thanks to those safety glasses. your advice should reassure not intimidate or scare.

The topic of cutting/coolant fluid is an interesting subject, Ive got a white paper somewhere explaining the pros, cons and new formulas involved in the wizardry of such stuff. I will try and remember to attach the PDF to the post.

[PJs]

Some funny lines in your write up MeJasonT! I'm glad this is taking off!

Perhaps for noobs and novices, the best lesson I learned on my mini (Peanut) was to take a touch off bite first then take a light pass to see the finish and how tough the material was. Granted the mini is a manual peanut, which allows you to "Feel" whats going on. It's definitely a light hobbyist machine which I knew going in, but I have worked some very small stuff cleanly down to 2 tenths up to large stuff like the grey bar. I'm not in production so time taken with smaller passes is ok with me, but repetition to work a big hunk to a small hunk can take it's toll on you. Besides whether its for production or home-hobby, quality is king for me, Always. The other thing to consider smaller passes is you may only have the one piece of material just big enough, so you don't want roach it trying to hurry.

This is a shaft extension with tight tolerances and a 50thou hole for press fit in the end that I built for a solar powered music box for my grandson. I was shooting for .2002 and undershot...oops, but it worked fine. Just takes patience and some time.



When I first started with it I watched a lot of Mr. Pete, Abom79, and Keith Fenner on YT. I saw these guy ripping off 100-200thou passes using carbide tools without blinking or Binking [no tool pieces to the forehead ;-P] and here I was happy to get 20-30 on aluminum...maybe. Keith taught me a lot and answered my questions graciously, particularly about carbide tooling, and I learned a lot about speeds and feeds from them all. The important upgrade for me was the QCTP I got and the TCMT carbide tool set I got. They worked on most things I did, and found the speeds and feeds a bit more flexible depending what I was doing. But found that in some cases the carbide bits just didn't "get er done" the way I wanted or needed.

I scrounged around in one of my old tool boxes for some HSS bit I knew I had but hadn't used or seen in years. After some practice grinding again after years of not, I found how much I liked what I was able to achieve with them. The mini plays well with most materials using HSS and now after time have built up a collection of various grinds I've needed. Mainly for me it's the finish I can achieve, minimizing followup finish work. But, I use the TCMT's quite a bit for getting through material quickly and reasonably well.

Probably the second most helpful thing I learned about (other than do Not Tax the machine) which John (hemmjo) brought up some really good points about angle of attack, Rake/relief and radii...and honing. I hone all my bits including the carbide (after some use) either with a stone or extra-fine diamond, it makes a huge difference in life, finish and feed rates, imho.

Coolant is a big subject as well and a lot of opinions about it out there. On the Drill Machines I used a water soluble that we used on the Mori in the shop and it worked great as long as I could get the guys to change it before it started smelling like a swamp of dirty gym socks. For me on the peanut, I just use a standard cutting fluid I picked up somewhere and WD40 and generally sparingly (unless parting) with a small squeeze bottle (drips), depending on the operation and mainly on steel only. Don't like acid brushes much but use a 1" throw away or tooth brush when working dry.

Whelp that's another 6 bits from me and my thoughts as a wanna be, when I grow up to be a Doug.

[ncollar]

PJ
I think you are doing just fine and maybe already have your Doug bars.
Doug has all the special toys.
Cheers
Nelson

[PJs]

PJ
I think you are doing just fine and maybe already have your Doug bars.
Doug has all the special toys.
Cheers
Nelson

Thank You Nelson that is most kind! I still think of him as "The Metal Whisperer" and feel his little finger probably forgot more than I have time left to learn about machining. I would like to have some of those special toys though, to test my bars so to speak.

PJ

[ncollar]

PJ
I totally agree.
Nelson