Messages

741

General Mach Discussion / Re: Anyone Here Have Experience Milling 6061-T651 Wrought Plate?

« on: January 19, 2010, 09:32:54 AM »

Here Ya go Ray, the way it's done.....

Now that's impressive!  How did you manage to NOT break it?

Regards,
Ray L.

742

General Mach Discussion / Re: Anyone Here Have Experience Milling 6061-T651 Wrought Plate?

« on: January 18, 2010, 07:30:50 PM »

I don't need an excuse like "too fast" or "no coolant", I just drop my carbide on the floor or the table and break the edges off....

Dropping on the floor is so low-tech, and manual.  I just let Mach3/SmoothStepper jam the tool through my touchplate, or ram it into the side of the workpiece when probing.  :-)

Regards,
Ray L.

743

General Mach Discussion / Re: Anyone Here Have Experience Milling 6061-T651 Wrought Plate?

« on: January 18, 2010, 09:08:39 AM »

Simpson,

You're absoutely correct.  My mistake seems to have been in mis-interpreting the tool manufacturers chipload recommendations.  My assumption was they provide recommended chiploads, but I now think they are more like minimums, and you need to go up from there, and see what you can get away with.  I have been running for a long time on values derived by calculating RPM based on SFPM, using the manufacturers chipload to calculate feed rate, then testing to see how deep I could go.  But yesterday I instead started with a shallow cut, and greatly increased chipload.  I found running MUCH higher feedrate did the trick with the icky material. I can run the same DOC (0.175"), but at a 30-50 IPM feedrate, and get an acceptable result, even without coolant.  I need to do more experimentation to come up with optimal values.

Regards,
Ray L.

744

General Mach Discussion / Re: Would like opinions on servo motor voltage and PS secondary in series

« on: January 17, 2010, 04:06:12 PM »

My new mill has a 90V servo motor for the spindle.  My current PS is linear 72V with dual rectifiers. The PS will be overloaded with the new spindle motor and the 4th axis motor, so I am contemplating buying a second PS and I am in something of a quandary of what to buy. The 90V motor runs OK on 72V, but does not achieve the speed I need.

I have axis motors running fine at higher (in one case double) than their rated voltages and I was looking for opinions on where to run a 90V spindle motor and what ramifications if any I would encounter running the motor at 130V

Also I see that dual rectifier PS can have the secondaries wired in series or in parallel for double volts of double amps. I am wondering in this case if it is possible to run one motor by taking the power in series and still be able take the regular voltage off the respective rectifiers. For example, can a dual rectifier 80V SP supply 160V for one motor and 80V for other motors by taking power from a series wiring for the HV and straight into each rectifier for the 80V?

Doesn't sound wise to me.  For one thing, motors have voltage and current ratings for a reason - if exceeded, the motor can fail, sometimes spectacularly.  Increased voltage also implies increased current, which, in a servo motor, can cause demagnetization.  It also means increased heat, and servo motors are usually not intended for continuous heavy use, so not vented.  As for "ganging" transformers, that can be risky, as someone pointed out.  You're much better off buying or building a single power supply suitably sized to your application.  Lotsa good transformers and power supplies available at very reasonable prices from antekinc.com.

Regards,
Ray L.

745

General Mach Discussion / Re: Anyone Here Have Experience Milling 6061-T651 Wrought Plate?

« on: January 17, 2010, 01:29:49 PM »

7075 can be cut dry in any hardness and it's similar to mild steel in strength.

2011 (bar) and 2024 also cut nicely. Like 7075, these very nice to cut after figting with 6061 or 5052 (which is even worse), although that joy comes at twice the price of the 'every day' grades.

2 flute cutters definitely help if you have the power and rigidity to make a big chip.  If you look up cutting speed for aluminum in any text older than a few years you will see what is today a very low number. Aluminum is routinely cut many times faster than that today, and one should get their cutting speeds from the toolmaker and also not forget to multiply that by the appropriate number if using cobalt, carbide or coated tools. You will find an indication for 3x to 10x faster speeds. I  run my 5/16" and 3/8" three and four flute cutters at 7,500 RPM . . . . only because that is as fast as my spindle would go.  My new mill is set up for 8,500.  1/4" cutters are the 'crossover point' below which I go to my die grinder spindle with speed set appropriately up to 28,000 for the really small cutters.

Of course, the faster you go, the more heat problem you have and you start to get into water cooled spindles and stuff like that.
   

I was wondering if trying more "high-speed machining" techniques might help.  I find it interesting that small cutters (1/8" and 3/16") seem to work fine, at the same RPM, DOC and feed I normally use, but the 1/2", both HSS and carbide, seem absolutely unforgiving, even at greatly reduced feed and DOC.  I'm tempted to try a 1/2" endmill running max RPM (8200), shallow DOC (maybe 0.050"), and high feed rate (probably 30-50 IPM?).

Regards,
Ray L.

746

General Mach Discussion / Re: Anyone Here Have Experience Milling 6061-T651 Wrought Plate?

« on: January 17, 2010, 02:13:07 AM »

Hey Ray, I get 4584 RPM for the 1/2 HSS 3 flute at 41.26 IPM.

See if this link helps you any.

http://precisionchaos1.com/support.htm

Brett

Brett,

The HSS tool is a 2-flute.

Regards,
Ray L.

747

General Mach Discussion / Re: Anyone Here Have Experience Milling 6061-T651 Wrought Plate?

« on: January 17, 2010, 01:50:47 AM »

What's odd is, I cut some smaller features, using 1/8" and 3/6" uncoated HSS 2-flutes, 8K RPM, 10 IPM, and they came out OK - Not great, but OK, and the cutters didn't seem to be damaged.

Regards,
Ray L.

748

General Mach Discussion / Re: Anyone Here Have Experience Milling 6061-T651 Wrought Plate?

« on: January 17, 2010, 01:49:19 AM »

Ray, I've used 2 flute Carbide with flood coolant and gotten pretty good results. Coated carbide does a little better. Can't remember using an HSS. What kind of feeds and speeds are you running? Cutter type, diam. and number of flutes? Make sure nothing is vibrating.

Brett 

Brett,

I started with a 1/2" 3-flute carbide, 5000 RPM, 0.325" DOC 30 IPM, heavy mist coolant.  It loaded up and broke almost instantly.  I then went to a 1/2" HSS uncoated 2-flute, 3100 RPM, 0.175" DOC, 10IPM, very heavy mist coolant.  It didn't load up, but the cut quality was awful, and after cutting about 24", the tool was destroyed.

Regards,
Ray L.

749

General Mach Discussion / Anyone Here Have Experience Milling 6061-T651 Wrought Plate?

« on: January 17, 2010, 12:21:17 AM »

I tried to machine some 6061-T651 wrought plate today, with rather disastrous results - four broken/dulled endmills later, I'm stumped.  If I go fast, the tools load up and break in seconds.  If I slow down enough to not get chip welding, the tool edges get destroyed VERY quickly - I ruined two brand-new high-quality HSS endmills in less than 24" of cutting each.  All the cutting edges were absolutely destroyed.  How the heck do you machine this cr@p?

Regards,
Ray L.

750

General Mach Discussion / Re: USB and Mach

« on: January 15, 2010, 08:12:17 PM »

Do you have the SS inside or very close to the computer? Thinking maybe your heatgun is heating the mobo as well as the SS and really the problem lies in the mobo.
Hood

Hood,

The SS is right next to the computer, but I was careful to heat only the SS - the heat gun was directed away from the computer.

Regards,
Ray L.