Author Topic: Lathes and stuff  (Read 21415 times)


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Re: Lathes and stuff
« Reply #30 on: July 08, 2009, 04:36:55 AM »
As a professional machinist I use around 95% carbide tooling and maybe 5% HSS. If you are using HSS by all means go with the the cobalt grades. They are much tougher and hold their edges longer. The minus part is that they are a bit tougher to grind. It is absolutely essential to have a properly dressed grinding wheel. A dressed wheel grinds easier and with far less heat buildup in the tool being ground. Use a medium to fine grit wheel on a quality grinder, such as a Baldor or other industrial grade grinder. The cheap imported grinders have flimsy tool rests and guards and typically won't have the power to keep the rpm of the wheel up and may have disappointing results. Cheap, lightweight tools won't hold up like a quality tool will.

As for the "junk" carbide cutters, it is probably more a problem of selecting the wrong grade. I use many imported inserts with excellent results. Here is an explanation of the grades.

C2- A bit softer grade with high abrasion resistance, used mainly on abrasive materials such as cast iron. This grade is also excellent for non-ferrous metals such as brass, bronze and aluminum, although aluminum tends to weld itself onto the carbide unless used with a cutting fluid. Kerosene works great and is much cheaper than store bought cutting fluids for aluminum.

C5- A general purpose grade that is useful in roughing and limited finish work. Its abrasion resistance is as its grade suggests, between C2 and C6. It will take a light interrupted cut but no carbide grade excels in this case. HSS is the way to go on interrupted cuts. C5 gives a reasonable good finish and is more forgiving of inexperience than the C6 and C7 grades.

C6 is a general purpose grade that gives a superior finish as compared to C5. As the grade numbers go up the carbide becomes less abrasion resistant and more brittle, but harder. This serves to hold the cutting edge longer and also allows the machining of harder metals with a slicker finish.

C7 is recommended for finish work. It generally doesn't hold up for roughing and will chip easier than the lower grades. This grade is commonly used in CNC work as a dedicated finishing tool for removing small amounts of metal at high speeds.

This is just a general recommendation and many jobs will require modification of the feeds, speeds, and depth of cut. This only comes with experience. I once had a sigh in my shop that someone had given me. It goes like this:

"We use good judgment in our work"
"That judgment came from experience"
"And that experience"
"Came from using bad judgment!!!"

Seriously though, there is a steep learning curve to contend with, and just having a lathe or a mill won't make you a competent machinist. You'll also need tooling, which in many cases will cost more than the machines themselves. You'll also need an analytical mind and a lot of patience. Math is as necessary a tool as a wrench or a cutter.

Many poor results of machine work are the result of improper speeds and feeds. To calculate any mill or lathe tool speed the following formula applies:

4 X SFM/diameter.

HSS tooling is most commonly used in the 40-80 surface feet per minute range. Carbide ranges from around 200 sfm to 600+, depending upon the material. I have just barely scratched the surface with these few hints, but these will help you get started with the results you need.

 Have patience and above all, HAVE FUN!!

Mike Montieth
Rutherford Machine


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Re: Lathes and stuff
« Reply #31 on: July 09, 2009, 07:56:23 PM »
Agreed, in the professional world it's got to be carbide. 
I got my start on a lathe in high school also, but I didn't pursue it as a career.  They taught with HSS so I've stuck with what I know.  Some carbide I've tried was pretty disapointing, but as RAB said maybe it was junk.  On the other hand I've borrowed a friend's brake lathe occassionally which uses a carbide cutter with excellent results.  So I guess, you pays your money and makes your choice.
All the best,

Being proficient with HSS is a good thing. If you ever get the chance to acquire a good carbide insert/holder turning facing tool with a couple of the proper grade carbide inserts they well be priceless if you have to turn something hard. Mike gives a good explanation of the carbide grades in his post. In our business we machine lots of Tungsten and other refractory metals. Carbide is tungsten with varying amounts of cobalt powder mixed in at the sintering process to create the different grades. We can accumulate a 5 gallon bucket of inserts in a short time. We can have the end mills reground for other uses but turning tools aren’t worth the time and money

Wisdom is remembering all of your Fuk ups!

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Re: Lathes and stuff
« Reply #32 on: July 10, 2009, 06:03:28 PM »
This is what I love about this forum, is that occassionally I get some really usefull information or ideas.  Thanks guys.


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Re: Lathes and stuff
« Reply #33 on: July 17, 2009, 02:17:53 PM »
As a machinist I have to disagree with a couple of post here ,

 To anyone that thinks you cant bore a cyclinder with a lathe and that crankshafts cant be made and or turned on a lathe then you are simply ignoring the history of engine manufacturing thru the ages.  Yes specialized machinery geared towards cylinder boring and crank turning has been developed and become the norm because of the ease of setup with multi cyclinder engines  but lathe boring of cylinders and crank turning is a very common process .

As far as crank turning it is commonly done on a lathe , crank lathes have become more specialized with offset fixturing  to turn individual crank pins  (to speed things up and stay profitable) but the lathe is still the machine used . There are tool post grinders avail to produce fine finishes on journals. I have turned and ground ALOT of cranks on the lathe .

I think the key to this discussion is that experience is whats required to make/repair good useable engine parts on an engine lathe .

 I can set a cylinder up in the sunnen boring machine and produce a perfect dimensioned and properly cross hatched bore in a few minutes but its not much harder to do the same thing on the lathe , just more time consuming and requires a hone and drill press to finish up.  There are two ways of Boring the cylinder in the lathe both of which have been around longer than the IC engine , If its small diam with a shallow bore length you would simply clamp the cyl on a face plate , spin it and use a boring bar. If its a large or deep hole you would mount the cyl on the saddle of the lathe and place a boring bar in the chuck and support the far end of the bar with the tailstock . There are micrometer adjustable boring bars for just this purpose . its the same method currently used to bore main bearing journals and cam journals in auto engines

Since specialized automotive machine tools have become more common over the past 30-40 years I think most folks forget how this work was done for the first 60 years and is still done in third world countries . You also need to keep in mind the engines we are discussing here all predate (in design) modern cylinder boring and crank turning machines. Sunnen wasnt around when the engine was born and somehow they got along just fine all thru the steam era and IC engine birth just fine.

Also wanted to mention rigidity is key to using carbide tools , as Jens mentioned carbide requires a fair bit of pressure and is alot harder to get a smooth finish with than HSS . I have a small (14x40) cnc lathe we use hear for odd jobs and I commonly use carbide for roughing and finish up with HSS as the machine is just not rigid enough for a fine finish pass of .0005 with Carbide . I also have a 16k lb slant bed 30hp lathe and due to rigidity it will make a finer cut than the smaller machine no matter what the setup, tool or material being cut .


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Re: Lathes and stuff
« Reply #34 on: September 06, 2009, 02:43:46 PM »
An area I find interesting is putting metal back on to cranks, etc.  Using a D-Gun, arc spray or laser cladding.  Also laser hardening and surfacing, diamond like coatings,  anodizing, nitriding, etc.

« Last Edit: September 06, 2009, 10:00:28 PM by jzeeff »


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Re: Lathes and stuff
« Reply #35 on: September 06, 2009, 03:39:03 PM »
I imagine we will be looking at adding metal to our Listeroids' cranks when the parts supply dries up.
I was thinking that these are the ultimate DIY engine because you can adapt what you need to keep them going.
With a mild steel crankshaft, you can stick weld it as a last resort. Hammer it true, lathe it smooth and put it back to work.???
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