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View Full Version : Suggestions for hogging on a small mill



wshelley
05-23-2008, 01:02 PM
Hi guys. I've got a MicroMark mini mill and I need to removed .125" from a dozen 2" wide pieces of 6061-t6. I have one of the small 2.5" face mills from grizzley. I can take about .010 per pass which means a whole lot of cranking. Any suggestions on alternatives to speed up the process with a small mill?

Thanks,

Ward

Ian B
05-23-2008, 01:31 PM
It probably depends on what's stopping you from taking the whole 0.125 in one pass. Is is spindle torque, or is it rigidity / vibration?

Is the 2.5" face mill carbide tipped, do the tips have rounded corners? You may be better off with an HSS cutter with square edges and high rake teeth. Cutting fluid would also help.

Ian

dp
05-23-2008, 01:33 PM
I've successfully used a battery-powered drill motor to power the table. Not precision, but it saves a lot of elbow grease.

carlquib
05-23-2008, 01:46 PM
Can you saw closer to size? If not then one of the roughing endmills, not sure how much horse power you have so you will have to pick the size that will work best for you. The corn cob roughers let you remove material much faster on a small machine and cut down on chatter.

-brian

Mcgyver
05-23-2008, 01:48 PM
I'm trying to hold back on .125 in AL and hogging being used in the same post :D :D

seriously though, for a mill that can only take off 10 thou in AL, 2.5" seems like a huge cutter, have you tried with say a 1/2 end mill? do it in one pass and then a finish cut of .005 with the big cutter

as a sort sidebar on the theory, think of the limitation on a machine as being the cubic inches of removal per unit of time its capable of. The constraint is created horsepower and/or rigidity. if you're there at a .010 DOC that the machine just can't take it anymore, ie the spindle stalls or its trying to shake itself off the bench, then you're getting to its removal rate limit, the volume of material it can remove per minute. Removal rate isn't something you calculate or are even going to read much about, its just a way of thinking and understanding how the balance how speed, feed, DOC etc work.

go more DOC, and you have to slow the feed. smaller cutter, more depth, keeps the feed the same, but you take more passes. Still will come out about the same material removal rate. Often I will go huge on the depth cut and slow down the feed to compensate logic being more of the cutter gets used (and worn) than just the bottom 10 thou.

this assumes you're going at a correct speed, cutter geometry is appropriate and the setup is rigid.

pcarpenter
05-23-2008, 03:02 PM
Many would argue (and have right here) that that 2.5" face mill is about the max for a mill like a Bridgeport...much less the mini-mill. I have used such cutters in my mini mill and its OK for a very shallow facing cut, but any way you figure it, its a face mill and not intended really for hogging off stock --even in a larger mill where its more appropriate. The reason is that as you plunge to a depth past the corner of that TPG insert, there's nothing to cut on the sides, so you are chewing your way through the work rather than shearing.

You can take quite a bit more with an end mill which is sharp on both the end and side and others have already recommended roughers as taking less horsepower to get the job done.

In any case, remember you have a mini-mill and be willing to work within its constraints. Its a useable tool if you respect its limitations.

Paul

wshelley
05-23-2008, 04:21 PM
Thanks for the suggestions, I was wondering about a rougher. I have a small, 3/8" I think, rougher so I can give that a try.

A few answers to questions. The carbide inserts have a small radius and I'm using WD-40. I can't cut any closer with my current tooling. The blocks were roughed out on a table saw with a non ferrous cutting blade. The stock left to be removed is actually from the thickness of the stock and I think it would be a bad idea to try a "dust" cut with the blade.

The DOC is more limited by my gut than the HP of the mill. The transmission has a sacrificial plastic gear. I broke the gear using a nice sharp fly cutter (about the same diameter as the face mill). It never crashed or stalled, I think the gear gave up due to the intermittent hammering.

I thought I should put a smiley next to the word "hogging" :rolleyes:

I have tried the cordless drill and might end up using that. I'll also try Mcgyver's suggestion of the larger DOC and slower feed rate. I have a few extra plastic gears if it goes poorly. My last thought is to use my son as a power feed...

Ward

pcarpenter
05-23-2008, 04:41 PM
I made myself a replacement key for the keyway in that plastic gear. I made it out of (IIRC) 1/8" square brass tubing. It should crush before the gear goes, although I have not torn up either one yet.

I have it on my list of stuff to make a belt drive for this mill, although I find I am not using it much now that I own bigger mills and may sell it first. Its an acceptable little machine within its limits. The trouble is that its often the first mill for a lot of guys and so knowing what reasonable limits are for a diminutive machine is a bit difficult. I have heard from some guys who tend to think like they are using a router table (on wood) and that't a recipie for broken stuff when learning to use metalworking machinery:D

Independent of rougher vs. standard end mill, you will find that a cutter that actually cuts or shears rather than plowing its way through work like that face mill will take quite a bit less horsepower-not to mention the difference created by using a cutter more in scale with the machine.

You mentioned a flycutter....they are really a bit hard on spindle bearings too since they hammer so much. The ideal cut is one that is not interrupted by running on and off the work.

Paul

bobw53
05-23-2008, 10:50 PM
I haven't cranked handles in a while, but a 2.5" face mill will put a hurt on even the most rigid cat40 machines when pushed.

From my experience, this is an instance where you need to listen to the guys praising HSS. Not so much for the HSS aspect, but the geometry aspect. I'm guessing any indexable mill made by grizzly(actually pretty much anybody) is going to be fairly neutral with a honed edge, not what you need to get the job done effectively. Horsepower eater.

Go with a 3/8 or a 1/2" endmill, as has already been suggested. Endmills have a nice high positive geometry and even the ones made for heavy hogging in steel only have a slight edge hone(much less than a standard milling insert). This will use a lot less HP, and create a lot less tool pressure, and let you get after it.

Don't discount the variable flute carbide endmills, they are beyond amazing on high HP rigid machines, but they are absolutely brilliant on low horse floppy machines.

Greg Menke
05-23-2008, 11:40 PM
I have a 3" shell end mill on my 40 taper Nichols, quite pleasant to cut with (will improve once I get it sharpened- edges are a bit of a mess), production feeds give a very real sense of the cut. Its quite interesting to feel how the metal is being removed- feed turns into how much pressure to apply to the feed lever relative to how quickly the metal is cut away.

Have taken .4" by 1.5" or so cuts in cast iron without drama, though using HSS w/ considerable rake. Don't have any 0 rake tooling to try. But I think a Nichols is a step up in stiffness & HP from the mills in question here.

Flycutters are not a big deal as long as the d.o.c. is light and rpm is reasonable given the work, cutter and sfm. Carbide will do fine if you go easy on it.

OTOH if the machine has plastic gears in the spindle drivetrain you'll have to treat it gently anyhow, would consider "hogging" out of the question.

Regards,

Greg

jkilroy
05-24-2008, 12:24 AM
I would suggest buying a much larger mill! :D You would be surprised what you can find cheap in the 5 ton range.

lwalker
05-24-2008, 08:09 AM
If the micro mark is the same as the HF mini mill you should have no problem with a 0.1" DOC using a 0.5" end mill. Make sure you have the speed right -- I tend to start off too slow and I'm always amazed how much better it cuts as I increase RPM. I regularly make cutouts through 0.125" thick cast aluminum boxes with a .125" EM in one pass and it goes nice and smooth.

Get the RPM right, use a big sharp endmill and watch your feed and it will go quickly.

wierdscience
05-24-2008, 08:26 AM
I highly recommend getting the belt drive kit for that mill,then you really could take that cut with a HSS flycutter.

The carbide face mill is too much for that mill for anything more than a .010" cleanup pass or so.

wshelley
05-26-2008, 05:29 PM
Hi Guys. Thanks for all the suggestions. In the end I increased the DOC and used a cordless drill. No hogging but lots of chips. Here is a picture of the face mill in operation:

http://www.wardscorner.net/images/CNC/ruckus/facemill_s.jpg

And a picture of the final parts:

http://www.wardscorner.net/images/CNC/ruckus/complete_s.jpg

The parts are for extending the frame on Honda Ruckus scooters. You can see more pictures on my website www.wardscorner.net

Ward