Indexable Carbide End Mill

I'm looking at R8 carbide indexable end mills from CDCO to use for cleaning up rusty stock and squaring up stock. One says it uses
tpg-32 inserts. Are those the same as tpg-322?
Another alternative is a similar 2.5" indexable end mill, which uses a different insert. SPG422 carbide Positive rake, 15 Degree lead angle I have a Bridgeport with the 2J head. Which of the two is more likely to give a good finish on hot and cold rolled steel?
What difference does the positive rake and 15 lead angle make?
Here's a link to the 2" one http://www.cdcotools.com/item.php?itemid 6
Here's the link to the 2.5" one http://www.cdcotools.com/item.php?itemidG1
RWL
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I would suggest you look at the price of the inserts - if you tool can use inserts without holes, the inserts are cheaper - look for a common size (like TPG-32 or the SPG-42) - look at a catalog on how to decode the number - T=triangle, P=positive, first number =diameter of inscribed circle in 1/8ths of an inch (e.g. 3/8), and so on - all of the on line insert company catalogs have a page or two explaining this - that will help a lot.
See what inserts you can get cheaply, surplus
<GeoLane at PTD dot NET> wrote in message

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On Fri, 18 Dec 2009 22:39:53 -0500, GeoLane at PTD dot NET <GeoLane at PTD dot NET> wrote:

Get a copy of the Enco [or another] catalog that has instructions on how to decode carbide specifications. http://www.michigandrill.com/catalog/view-mdc/173.pdf will get you started. for sale prices see http://www.use-enco.com/CGI/INLMK32?PARTPG=INSRAR2
TPG stands for "Triangular Positive Ground" TPU stands for "Triangular Positive Unground" [on the top], and is about the cheapest carbide insert available. For home shop turning and milling use these are generally entirely adequate. If possible buy a package [on sale] as the price per insert is generally much less.
Generally TPU/TPG inserts will have 11 degree side relief angles.
To decode the numbers TPGxyz x is the diameter of the largest circle that will just fit onto the insert in eights of an inch, thus a TPG3yz is a triangular insert that will just enclose a 3/8 diameter circle. y is the thickness in 1/16s of an inch. thus TPG32z is nominally 2/16s or 1/8 thick. z is the corner radius in 64ths of an inch. Thus as TPG322 would have a 2/64ths or 1/32 corner radius

SPG stands for Square Positive Ground" and the numbers are coded the same way. Note that you get an additional corner with the S inserts, but you may find out when you do a per corner cost that the TPUs are cheaper.

Long involved discussion here. You have to have positive rake inserts for the back of the tool to not drag on the work. While there are mill and lathe holders for negative tools, this generally requires more rigidity and power than the typical home/hobby machine. Moltrech among several others discusses the effect of lead angle on milling. (Amazon.com product link shortened) https://www.hanserpublications.com/product.php?ISBN 81569902738

Be reminded that you will [theoretically] need two grades if you machine both aluminum and steel. C2 for Aluminum and C5 or C6 for steel. However for the typical low volume low stress home shop machining more than likely either one will be perfectly satisfactory with both materials.
Given that you will be tending to chip and break the inserts milling rusty material, possibly with hard spots, I urge you to consider a fly cutter using HSS lathe tools. The cost is low and as you can resharpen the HSS tool bit on most any grinder or belt sander, this is one of the most economical solutions, particularly for the home shop where production and speed are not important.
Making a fly cutter was a traditional apprentice project, frequently with two HSS bits, one roughing and one finishing, however as you are just starting machining I would buy a single bit fly cutter set to start and then after you gain some experience and insight into the terminology such as axial and radial rake, you can build your own, sizing to fit your equipment.
For an import fly cutter set see http://www.use-enco.com/CGI/INSRIT?PMAKA=ST225-3035&PMPANO08087&PMKANO"2&PMKBNO88&PMPAGE&PARTPG=INLMPI if you want a fly cutter with an R8 shank see http://metalworking.mscdirect.com/CGI/MWSRCH?N@51 for a more elaborate fly cutter see http://www.kristitool.com/ktl/b-52.php
Let the group know how you make out.
Unka George (George McDuffee) .............................. The past is a foreign country; they do things differently there. L. P. Hartley (1895-1972), British author. The Go-Between, Prologue (1953).
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Thanks for all the info. It was nice to have some pointers to references as well as the voice of experience in what to look out for. I do have a fly cutter which I built way back when I bought my Hardinge Horiz / vertical mill 20 years ago. As a single point tool, it's slow to clean up stock and the RPM is slow as well since it's using HSS, that's why I was interested in the carbide indexable mills now that I have a Bridgeport. Fly cutters are indeed a low cost solution, with the tradeoff being time.
RWL
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On Fri, 18 Dec 2009 22:39:53 -0500, GeoLane at PTD dot NET wrote:

I am just adding to what the previous posters have said. The advice they have given is sound. I would only like to add the pros and cons to the two styles you are looking at. I am probably missing some, but:
Triangle inserts: pro: can face mill up to a square corner. con: slightly weaker and more prone to breakage. Lighter cuts will need to be taken. only 3 edges per insert.
square: pro: stronger, more heavy cuts can be taken. con: can't mill up to a shoulder(when used with the lead angle shown)
Of the particular holders shown, some things to consider:
a four insert tool will be faster that a 3 insert tool. Probably not a big deal for a hobbyist.
The square insert tool lead angle will slightly improve insert life and can be helpful on brittle materials to prevent edge breakage (of the workpiece). It also looks to have more axial rake than the triangle holder. This will improve surface finish, and is slightly easier on the machine. The triangle inserts seem to begin the chip with a maximum edge force, and the result is a noticable difference in the noise, in my experiences with the two types. It's probably harder on the machine.
Of the two, I personally would probably use the square insert holder 90 percent of the time.
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From what little research I have done, triangular inserts are a lot more common, and therefore likely to be cheaper due to availability surplus. I looked into this a number of years ago, so square inserts may have become a lot more common place by now.
eBay has 63 hits for "TPG", versus 39 for "SPG" under carbide inserts, so the square ones are certainly available these days.
Doug White
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