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dockterj
02-19-2009, 10:14 PM
I'm trying to get this smithy 1220 lathe/mill to be useful for something other than holding down the workbench. It's mostly done so I thought I'd try the mill out. I put a piece of 6061 scrap that was laying around (approx 3/8 x 1 1/4 x 8) in a vice and a 1/2" two flute HSS end mill in an end mill holder. The max RPM for the mill is 1600 so that was that. Well I'm finally making some chips but I'm very disappointed with the end result. I eventually got the surface finish to look passable (something that I could clean up with some 200 grit) but there are still too many marks in it. The worse part was that if I stopped the feed while the mill was still on it would cut a "dent" deeper than the rest of the milled surface. Is this normal? Without being able to spin at 4000 rpm what can I do to get a better surface finish? I'm cutting the smaller dimension (3/8 x 8) with the side of the end mill. I've got the cross slide locked and the quill is locked too. I'm using a little wd40 for lubricant. I thought maybe the quill isn't rigid enough so I put a dial indicator in a magnetic base and with the quill all the way out I measure +2 -2 thousands play pushing and pulling pretty hard. Does this seem like too much? I couldn't see if the play was in the bearings of the spindle or in the quill itself. Guess I need to look at that a little closer.

I'd like to start a real project but not if this is the best I can expect!

dan s
02-19-2009, 10:17 PM
get a cutter with more flutes.

Evan
02-19-2009, 10:36 PM
Plus/minus 2 thou is far too much. You might think you are pushing hard but tool forces are even harder. Suck everything in a close as possible and try that. Clamp the work directly to the table. Pull in the quill all the way and leave as little cutter sticking out as you can get by with. Slow down the feed and use a smaller cutter to minimize cutting forces. And, of course make sure it is in tram.

Ken_Shea
02-19-2009, 10:45 PM
While 1600rpm is not ideal there is no reason you shoul dnot get decent cuts.
Here are a few considerations.

1) Is this a good quality HSS cutter?
2) Better yet, get a 3 flute carbide aluminum cutting end mill.
3) Keep chips cleared X 2
4) Lubricant, I use flood but many find WD-40 very good even a mild air blast.
5) Climb Mill
6) Keep the cutter as short as possible.
7) Be sure stock is solidly mounted.
8) Don't feed to fast.

Ken

Circlip
02-20-2009, 06:04 AM
Climb mill??? Yep,that will show how loose your slides are, make sure you're wearing a bullet proof vest, full face mask and gloves.

Regards Ian.

Just Bob Again
02-20-2009, 07:27 AM
I'd like to start a real project but not if this is the best I can expect!

Depends on how good a machinist you are. Not the best tool, obviously. You have to use EVERY possible edge on a machine like that to compensate. Shortest possible quill extension. Best quality endmill. Work held as close as possible to the slide. A good vise. Cutting direction matters. A lathe carriage is not constrained the same way as a mill table. May need to shim the guides on the bottom of the carriage so it's tighter. Cutting forces on a lathe push the carriage down. Milling pulls it up. Lock the carriage and try milling with the cross slide. You have to reduce the slop bit by bit and see what works on your machine until it becomes acceptable. Side milling always has worse finish than face milling, even on a Bridgeport. How are you holding the cutter? The extra inch projection from an endmill holder matters. A collet keeps things closer to the spindle. You can do good work on a less-than-ideal machine. It's just harder and slower.

Evan
02-20-2009, 08:10 AM
What Bob said, best quality endmill, is vital. The difference between a cheap import cutter and the best from a long established brand name is night and day. Good quality cutting tools can make even a worn out or poorly made machine usable.

There is an old saying, "A poor workman blames his tools". That isn't always true but the converse is in my opinion. "A good workman uses good tools". I buy individual endmills that cost as much as an entire set of "China yellow specials". They also outlast an entire set of those cheap cutters and do a far better job when they are worn than the "specials" do when new. If you buy an endmill or two for use with aluminum then never use them for steel and they will last almost forever. One must have size is 4 flute 1/4 inch solid carbide endmills. I pay about $10 each for them and they are one of my most used cutters. The 1/4" size is strong enough that you will have a hard time breaking them and the superior rigidity of carbide goes a long way in preventing excess deflection of the tool.

JoeFin
02-20-2009, 08:22 AM
Try one of these

http://www.smithy.com/cnc1240.php

kvom
02-20-2009, 09:02 AM
You can also do a "spring" cut. After each pass conventional milling, reverse to clean up slightly. Definitely check the spindle tram.

Ken_Shea
02-20-2009, 09:02 AM
Climb mill??? Yep,that will show how loose your slides are, make sure you're wearing a bullet proof vest, full face mask and gloves.

Climb milling is done all the time on manual machines, there is just absolutely no reason to be paranoid about climb milling. You can't cut a slot with out climb milling.

Loose slides? that is why gibbs are adjustable.

Ken

dockterj
02-20-2009, 09:16 AM
wow! thanks for all the pointers. I agree that this is not an ideal machine but it is what I can fit in my shop and it is what I have so hopefully it will be better than no mill at all.

Dan - I thought that a 2 flute was better than a 4 flute. Maybe that doesn't apply to HSM especially with my slow spindle. I have some other end mills I will try tonight to rule the end mill out.

Evan - I agree that that sounds like the mill head isn't rigid enough. I'll take some more measurements tonight and will try to setup the material higher so I don't have to drop the quill so far. I think the tram is pretty close but I haven't worked on that yet. I thought that it wouldn't be a factor as I am not milling with the end of the mill, just the side, is that correct? Also, the finish seemed to be better the faster I fed the material but I'll try slower as well (also will try climb milling).

Ken - 1 - it's a used cutter but a good quality one. I've tried a couple different end mills with the same result but will try a 4 flute that is brand new and see what that does. 3 - yep - without spraying lube in the chips gall out the surface 5 - I haven't tried that yet - your right that should have been the first thing i tried. The screws are pretty worn but I've got the gibs snugged up good. 8 - ok any hints on knowing when I'm feeding too fast or too slow?

just bob - I'm using an end mill holder so that sticks out of the quill a couple inches along with the end mill sticking out of the holder. I guess this is why knee mills were invented, right? I'll see what I can come up with to get the material higher.

Thanks again for the advice! I'm a total newby so I don't know if it is the tool, the operator, the setup, the operator, the material, the operator or too high of expectations. I'll report back later.

ERBenoit
02-20-2009, 09:56 AM
wow! thanks for all the pointers. I agree that this is not an ideal machine but it is what I can fit in my shop and it is what I have so hopefully it will be better than no mill at all.

Dan - I thought that a 2 flute was better than a 4 flute. Maybe that doesn't apply to HSM especially with my slow spindle. I have some other end mills I will try tonight to rule the end mill out.

Depending upon what you are cutting and trying to accomplish.

While I'm not familiar with you particular machine, here are some basic rules. Disregard what doesnt apply.

1.) Keep your overhang to a minimum. Both the endmill in a holder or collet, plus quill extension, which should be minimal if any while milling. The more overhang, the more flex the endmill can take. This may be causining the "depression" when you stop and dwell in one spot.
2.) If you're hogging away material, a rougher is the only way to go.
3.)The more flutes, the more ridgid the endmill will be. This comes at the expense of chip space, with the exception of a three flute. A three flute will give you the same chip space as a two flute mill, yet will be more ridgid. A two or three flute endmill will give you the chip space that a four, six or more flute endmill lacks.
4.)Softer material, you can take a thicker chip, thus you need space for that chip.
5.) Four flutes are ideal for harder or more difficult to machine materials where chip thickness would be less or used for finishing cuts. The more flutes the faster the feedrate should be. IMO, a four flute should be used on aluminum for finishing cuts only. This page offers some tips:

http://www1.mscdirect.com/CGI/GSDRVSM?PACACHE=000000085571195

Carld
02-20-2009, 10:25 AM
I think you would get a better surface finish with a flycutter running about 1000 rpm. You will have to experiment with the feed rate.

With a 1/2" endmill it will be hard to not have a surface with tool marks and lines where the cuts overlap. What you need to do is cover the entire surface with the cutter and a flycutter will do that without being expensive.

Evan
02-20-2009, 11:09 AM
Here is a secret weapon for obtaining a super finish when side milling on a less than ideal machine. My mill has no problem even milling T1 steel but with this cutter it will take faster side cuts with better finish.

It's a tungsten carbide burr and you need this particular style. It needs coolant while cutting, I spray on WD-40. It works on both aluminum and steel and produces an almost polished finish. The swarf comes off as powder. It must be kept cool as it has many points of contact but it will work far better and in either direction in a relatively flimsy setup. It can take up to a .030" depth of cut in steel, more if you go very slow.

http://metalshopborealis.ca/pics5/burr.jpg

Tram will affect side cuts depending on which direction you are cutting and which direction it may be out.

Circlip
02-20-2009, 11:27 AM
Sorry Ken, I was just reading the spec that Docterj gave us, didn't realise that part way through the job he'd changed machines to one that had fully adjustable gibs and a rotational speed suitable for the size of cutter he's using. You forgot to tell him to take all the backlash out of the screws, better still fit ball screws.

Regards Ian.

Carld
02-20-2009, 11:30 AM
:o opps, I missed the side milling part of the post. Yes, side milling is always hard to get a good finish. The irregularities in the ground flutes would cause trouble and even taking a climb cut of a few thousandths may still leave a poor finish.

For a nice finish you really need to flycut it or use an insert cutter head that covers the entire surface or grind it.

Paul Alciatore
02-20-2009, 12:42 PM
I'm milling some aluminum on my Unimat right now. As a small machine, it can have many of the same problems. But full sized milling machines can also have problems if not used properly.

The surface variation you talk about is evidence of looseness in the machine/setup. I get the same kind of mark if I stop in mid cut.

1. Try locking down the gibs in any axis you are not actually moving along. This can help a lot.

2. Use a good cutting fluid. I like WD-40 for aluminum. It will improve the surface finish quite a bit. Others will do the same. Tap Magic for Aluminum is also good.

3. Try different feed speeds. Sometimes faster is better, sometimes slower. The gods of chipmaking.

4. Yes, as others have said, good tools. Evan's cutter looks like something I want to try. But it would not be good for heavy cuts. For heavier cuts I use a two or at most a three flute cutter.

5. Faster spindle speeds generally produce a better finish. But you are limited by your machine. You could use a slower feed to try to compensate.

6. Always avoid climb milling when initially making the cut. It will pull the work into the cutter in uncontrolled jerks and a good finish will be almost impossible. You would probably break the cutter sooner or later.

7. But do try the reverse direction feed for cleaning up the cut. DO NOT increase the depth of cut for this. Leave it exactly where it was for the initial cut. You will get a slight dust from the cutter. You can't see it if you are using a cutting fluid, but it will be there.

8. Do not stop the feed while cutting. Easier said than done. You may need to replace or modify your handwheels/cranks if they are arkward. I am presently fitting steppers to my Unimat to avoid this problem. Initially they will be controlled from a simple manual panel that simply controls direction and speed. CNC will come later.

You can get a good finish. Also, a very fine abrasive paper on a flat can be used to clean up the tool marks. If you do this, allow a bit for it when milling. Also, do not use it too much as the part can become rounded instead of flat. Also not good for sliding surfaces as the grit can become imbedded in the part.

lazlo
02-20-2009, 12:48 PM
Here is a secret weapon for obtaining a super finish when side milling on a less than ideal machine.

It's a tungsten carbide burr and you need this particular style.

That's interesting Evan. Marv Klotz uses those in his rotary milling jig.
Is that a double-cut burr?

MSC is having another 35% off sale today, so the Atrax 3/8" double-cut carbide burr is $12.64:

http://www1.mscdirect.com/CGI/NNSRIT?PARTPG=IMLMKD&PMPXNO=2210141

Evan
02-20-2009, 02:08 PM
That's a product photo I found. I'll go take a picture of the one I use. I tried some other different ones and they didn't work well at all so it seems to be very important to use the right type. Back in a bit.

Evan
02-20-2009, 02:27 PM
This is the burr:

http://metalshopborealis.ca/pics5/burr2.jpg

This is a cut I just now made in the side of half inch mild steel at 2 ipm and about .020 doc using WD-40 lube. Only a single climb cut pass from right to left, no spring pass or finishing cut.


http://metalshopborealis.ca/pics5/burr3.jpg

Carld
02-20-2009, 03:09 PM
Yes, but the surface finish would be much better with a fly cutter. The only time I would side cut is if there was no way to do a flycut on the surface.

No matter what kind of endmill or burr you use the finish will not be as good as an insert cutter head or flycutter.

S_J_H
02-20-2009, 04:04 PM
I'll have to give one of the carbide burrs a try. I have several of them saved from when I dabbled in cylinder head porting. Used them with a die grinder and plenty of rpm. Never thought to pop one in the mill.

I vote for the fly cutter as well. I have been using ccgt style turning inserts in my flycutter, It's like a mirror finish almost.They work great in iron as well.

Evan
02-20-2009, 04:49 PM
No question the fly cutter will produce the best finish. But, the burr will work well even in a very shaky setup which is why I brought it up. It doesn't tend to chatter at all.

For the burr I run it at only 1000 to 2000 rpm otherwise it will overheat. Even then it needs cooling.

lazlo
02-20-2009, 07:45 PM
Yes, but the surface finish would be much better with a fly cutter.

A fly cutter leaves a very nice finish, but you get those overlapping circular mill marks. I like that kind of finish, but a facemill with a wiper insert will leave a mirror finish.

The middle stripe is my reflection in a cast iron surface plate I faced with Sandvik shear mill, with one of the inserts replaced with a wiper insert. The upper and lower "stripes" hadn't been finished yet (the surface plate was bigger than the Millrite table, so had to do some hinky setups):

http://i164.photobucket.com/albums/u15/rtgeorge_album/SEHInserts016s.gif

dockterj
02-22-2009, 06:03 PM
thanks for all of the great help! I've got a pretty good finish on side milling now. I blocked up the vice so the quill isn't extended and used a 4 flute end mill in better condition. I also did a "spring cut" climb milling back out of the cut and the finish is as good as I could hope for from this machine. I tried end milling and the finish is ok but I think the tram is off slightly. While trying to set the tram I found the table has a "wedge" to it. A test indicator in the quill shows a rise of a few thousandths while moving from side to side (ways) but nothing going in and out (cross slide). I'll have to figure that out before I trust any measurements on the tram.

Thanks again for all the advice!

J Tiers
02-22-2009, 07:52 PM
I'm trying to get this smithy 1220 lathe/mill to be useful for something other than holding down the workbench.
Well I'm finally making some chips but I'm very disappointed with the end result. I eventually got the surface finish to look passable (something that I could clean up with some 200 grit) but there are still too many marks in it.

Your surface speed is 300 fpm, which is low end for aluminum, but not stupid. Some aluminum is sticky and will finish poorly. Real 6061 ought to be OK, I do fine much slower than that speed.

Sounds like you have had flex and give in the spindle.



The worse part was that if I stopped the feed while the mill was still on it would cut a "dent" deeper than the rest of the milled surface. Is this normal? Without being able to spin at 4000 rpm what can I do to get a better surface finish?



This is definitely due to a limber and flexible machine...... a wet noodle...... it is flexing away from the work, and you'll never get decent work out of it unless you can tighten it up, or you take really tiny cuts..

Tighten everything. Forget you have a quill feed, and lock it in "up" position.

Added.....I went and looked at the website..... Smithy Midas 1220?...... that thing has so much daylight, and so big an overhang from the tiny "pencil-neck" column to the head, that I would expect some significant flex, chatter, etc.

How low can you get the head without lowering the quill?

C.BRAXMAIER
02-22-2009, 11:59 PM
Climb milling is done all the time on manual machines, there is just absolutely no reason to be paranoid about climb milling. You can't cut a slot with out climb milling.

Loose slides? that is why gibbs are adjustable.

Ken
True that:D

jkilroy
02-23-2009, 08:55 AM
If you are cutting with the end of an endmill, one thing that helps surface finish a great deal is to use a tool with a radius on the tooth. Just make sure the feed is not so fast as to be larger than the radius per revolution and you can get great finishes. All roughers have a radius on the tooth so they are good for this. Another plus is you are much less likely to break a tooth that has a radius.