Gunsmithing A couple more machinist questions

[shadow_sniper]

Where do I find SFM? I have googled it but I cant find anything half way specific for aluminum. I have seen a range of 200-1000. Thats pretty big. What is a good solid number for cutting 6061 with Tin coated HSS speed end mills?

Should my RPM change when using a rougher?

Would it be possible to use a diamond cutter in a bench top machine for aluminum?

What is the best way to cut a 45 degree angle with out using a sine plate?

 

[Luvman]

Re: A couple more machinist questions

Your best bet for aluminum is as fast as you care to go and can keep the material from galling to your cutter. 600 SFM is a good number . Skip the roughing endmills. 2 flute endmills do great. The 3 flute YG carbide aluminum endmills are best I've tried. Use WD40 for lube. Skip mineral spirit kerosene mix.

HTH,
LM

ETA: skip 4 flute endmills with aluminum. They have less room for chip evacuation. As to the 45* you can use the head of combination square if your set up has room.

 

[300sniper]

Re: A couple more machinist questions

i highly recommend picking up a copy of "machinery's handbook". everything you ever wanted to know and more is in that book including feeds and speeds. you can also download "machinist mate" online. it is very basic and will help you pick a speed and convert it to rpm depending on material, cutter type and cutter diameter.


edit: fyi, machinist mate recommends 450 sfpm for coated hss in aluminum.

 

[shadow_sniper]

Re: A couple more machinist questions

I have looked into the handbook, but a 70-90 dollar book is little out of my price range. I will look into the the machinist mate.

so at 600 sfpm I would be running at 4584 RPM. Thats like double what I am running at know. 450 sfpm is still 3438 rpm.

 

[300sniper]

Re: A couple more machinist questions

if it is a small benchtop manual machine, maybe try a basic non-coated 2 flute hss endmill at 300 sfpm. it sounds like you are using a 1/2", try 2300 rpm.

600 sfpm is a good speed in aluminum for carbide but i doubt you would be able to feed fast enough on a manual machine to keep up with it.

 

[JWArmory]

Re: A couple more machinist questions

375 according to redline. If I were you I'd junk the HSS and go on Ebay and pick up some carbides. GW Schultz usually has a bunch of extras for cheap there.

 

[Powder_Burns]

Re: A couple more machinist questions

Whats the current edition of Machinery's Handbook? I'm starting to wrap my head around all this stuff, I got the 13th edition in my lap published 1946, I think it might be a little out of date?

 

[300sniper]

Re: A couple more machinist questions

i have the 27th edition and inherited an 18th edition in perfect condition. i usually work out of the new one and keep the old one safe and clean in the house. some things are easier to find and less complicated in the older version. the other day i was looking for the "unit power" of different material in an attempt to figure out required horse power for a cut. i couldn't find this information in the older one. the newer one had this it though.

 

[skog]

Re: A couple more machinist questions

Think of this as the condensed version of the machinerys handbook. All the info is taken form the version 28. Cheaper way to get started and the smaller book is nice too.

http://www.amazon.com/Reference-Students...8343&sr=8-7

 

[scout67]

Re: A couple more machinist questions

I have bought several mach. handbooks off ebay. I have several different editions. Anything from the 23rd and up should be fine. I got mine for alot less than retail. RPM depends alot on the machine. I use koolmist or wd-40 for lube and cooling. I use hss most of the time. My manual machines don't have the rpms to require carbide. I do slow down with roughers. I use them for heavy cuts and they tend to do better for me at a little slower speeds. What diamond cutter are you refering to? Are you refering to carbide inserts? If so, that depends on the machine. I use a small diameter cutter in mine for light cuts. My bench top is really a lightweight. I use my other mills for most of the work. How you cut a 45 depends on what you are trying to cut and how much accuracy is needed. If I need a small 45 on a part I use hss cutter with 45 degree angle. For large 45s that don't require a lot of accurracy I clamp the part in the vise using a speedsquare to set it a 45. Otherwise tilting the head or if you have a vise with a swivel base you can set it to a 45.

 

[AWGunS]

Re: A couple more machinist questions

IF you buy good tooling from a reputable company, they all have customer service and tech's that you can talk to and ask questions. They are more than happy to help.


Machinerys Handbook is a bit daunting. But, you can find pretty much whatever you need to know with it. Find a copy and use it when you need it.

 

[slabsides52]

Re: A couple more machinist questions

SFM stands for Surface Feet per Minute. This is the speed at which the workpiece material is passsing the cutting tool edge. For a give diameter, the higher the RPM, the faster the SFM, because the workpiece material is moving past the cutting tool at a much higher speed.

The quick and easy formula for calculating SFM is RPM X DIA in inches X .26. This should get you close enough.

Different workpiece materials can be cut at different speeds due to the hardness of the material, the heat generated in the cut, the rigidity of the machine and set up, etc.

On a manual machine you will usually be limited by the speed at which you can react and manipulate the controls. On a CNC machine this all happens automatically, and operator dexterity is not a factor. Most manufacturer's higher speed recommendations are made for the CNC applications.

On a manual lathe you will probably find 200-400 SFM on alloy and stainless steel will be your limit, and a little faster on aluminum. Run the aluminum as fast as you can control the machine.

If your speed is tool high on turning or milling operations for the work piece material and cutting tool, too much heat will be created and the tool will burn up or dull quickly. If the speed is too slow, the tool will not effectively cut the material, but will tear it off and leave a lousy finish on the work piece surface.

For most gun smithing applications, you will want to use PVD or uncoated lathe inserts. These inserts have a sharp edge and will make lighter cuts without creating as much push off as CVD or honed edge inserts.

An old machinint's rule of thumb was "Double the speed and half the speed on a finishing cut", or "Half the speed and twice the feed on a roughing cut". The lower the feed, the better the surface finish (less threading on the part OD).

 

[lanwickum]

Re: A couple more machinist questions

I've been there before, but it still amazes me. Why do we get into things like machining when we can't afford a $80 book that tells us how to do it?

Good luck with your project. It is still fun if it doesn't get to frustrating with out good funds.

 

[300sniper]

Re: A couple more machinist questions

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: montana</div><div class="ubbcode-body"> Why do we get into things like machining when we can't afford a $80 book that tells us how to do it?
</div></div>

now there's a great quote!

 

[Raven 6]

Re: A couple more machinist questions

I agree, the machinist handbook is a must, there is more information in there than you can imagine. If anyone can spend thousands on a machine what is 80-100 bucks. In my personal experiance, on manual machines I talk in terms of RPM and IPR, which on a manual mill IPR is hard to determine with out a DRO, it's a feel thing for me, and that comes from experiance. On CNC machine I talk in terms of SFM and IPR. I think two flute endmills are better on aluminum for prior stated reasons. My best suggestion is to take a few machinist classes at your nearest community college, if you don't want to do that, experiance will be your best teacher.

 

[300sniper]

Re: A couple more machinist questions

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Triple 6</div><div class="ubbcode-body">I think two flute endmills are better on aluminum for prior stated reasons. </div></div>

i bought some m.a. ford 3 flute carbide endmills for aluminum and think they are the a great compromise. you get good rigidity and feed rates with 3 flutes and still have adequate space for chip evacuation. even in my small mill with only 1.5 hp, running a 1/2" endmill full cutter width, .050" doc, 4500 rpm and about 25 ipm is a cool sight to see with a rooster tail of chips flying off the part.

i am not sure you could take advantage of them with a manual machine though. i think with a manual machine, one would be better off with standard hss endmills. they are more forgiving than carbide.

 

[AJ300MAG]

Re: A couple more machinist questions

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">I think two flute endmills are better on aluminum for prior stated reasons. </div></div>

Can't agree with that...

We're talkin CNC now, with a corncob style rougher. First off I'd have to cut my feedrate in half running a two flute. Secondly the chips off a rougher are quite shorter in length, easier to flush out with high pressure coolant or airblast (with a little cooltool or WD-40 in the mix). The long chips off a finish endmill tend to bunch up and get jammed into stuff.

I'll run a rougher in a Bridgeport also. Might have to dial down the feedrate a little though I can increase the depth of cut/overlap without hearing the spindle motor groaning or the squak of a finish endmill...

Our Patternmakers like two flutes too. The also can't comprehend the concept of making cuttercomp a variable either...

 

[triggerguard1]

Re: A couple more machinist questions

If your radial depth of cut is not excessive, a 4 flute cutter will double your feedrate and produce a nicer finish, while thinning the chip and allowing it to flush better from the workpiece.

On a real piece of equipment, aluminum is 2000+ SFM. I run 416 stainless and 1018 at 800-1000SFM.

Adding anykind of a coating to HSS is somewhat of an exercise in futility. The substrate is simply not dense enough to take full advantage of the coating over it. The substrate gives, thus flaking the the coating off very quickly.
If you want to have coated endmills, go with carbide and don't look back. Dataflute and Skicarb are great carbide aluminum cutters and I've filled many chip buckets with both.

But before all of that technical stuff.......Get a Machinery's Handbook, or take up basket weaving. Seriously, if you can't see yourself investing in the bible for machinist, you've a long road ahead of you in this trade.