tool Chatter on 3-axis router

I'm new to high speed machining. I'm cutting a brass part
http://i1262.photobucket.com/albums/ii619/Modelbauer1963/Chatter.jpg
with a 4mm HSS Co TICN cutter. The surfacing works fine, but when I try to make a deep counterbore I get a really bad finish. I'm running the tool at 10k rpm (spindle range is 8k-25k rpm) and the finishing pass at F300. I'm not sure what my F values actually mean, like in ipm, but it looks like a g ood speed. I suppose my my options are to use a carbide cutter, go to 6mm d iameter (max on this spindle), or adjust the feedrate and spindle speed. Ca n anyone take a look and make suggestions? I know I should get myself a pro per knee mill, but that's not a realistic option for me at the moment. I'm hoping the machine I have
http://i1262.photobucket.com/albums/ii619/Modelbauer1963/CNC1.jpg will be adequate if I tweak the operation enough.
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I'm new to high speed machining. I'm cutting a brass part
http://i1262.photobucket.com/albums/ii619/Modelbauer1963/Chatter.jpg with a 4mm HSS Co TICN cutter. The surfacing works fine, but when I try to make a deep counterbore I get a really bad finish. I'm running the tool at 10k rpm (spindle range is 8k-25k rpm) and the finishing pass at F300. I'm not sure what my F values actually mean, like in ipm, but it looks like a good speed. I suppose my my options are to use a carbide cutter, go to 6mm diameter (max on this spindle), or adjust the feedrate and spindle speed. Can anyone take a look and make suggestions? I know I should get myself a proper knee mill, but that's not a realistic option for me at the moment. I'm hoping the machine I have
http://i1262.photobucket.com/albums/ii619/Modelbauer1963/CNC1.jpg will be adequate if I tweak the operation enough.
=========================I suspect you won't like what you see if you put an indicator on the head to measure deflection and pull on it with a spring scale.
I got a chainsaw finish from milling meter cutouts in 0.030" sheet Aluminum with a 1/4" end mill with flutes 2" long, which I was using to clear a forest of clamps. The reason was tool flex, not the machine; a 1/2" diameter cutter gave a smooth finish at the cost of more filing to square the corners.
My 700 Lb Clausing's spindle deflects ~0.001" per 25 Lbs.
-jsw
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On Fri, 13 Feb 2015 01:36:10 -0800 (PST), robobass

Brass likes to grab cutters -- they dig in if they have any positive rake at all. Zero rake or slight negative rake may solve your problem. On a lathe tool, that's easy. On a milling cutter, your options are limited. You can try dubbing off the very edges of the cutter with a small stone.
First try just giving it a little radius -- really small. If that doesn't do it, try honing a slight negative angle on the very edge. At those rpm, you don't have to hone more than a couple of thousanths back from the edge, because you aren't cutting deep to begin with.
Your machine and the coarseness of the chatter suggests, however, that any "digging in" is being amplified by a lack of rigidity in the whole setup. That's going to make it tricky.
Anyway, this is a cheap and easy thing to try first.
Cute kid, BTW.
--
Ed Huntress

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What is the make of the spindle on your machine? I've been looking for one of that size.
Hul

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On Friday, February 13, 2015 at 11:58:50 PM UTC+1, Hul Tytus wrote:

e
Sorry, I have zero documentation on the motor, and there isn't any sort of label anywhere on it. I bought the machine from a Russian guy who was very helpful walking me through the Mach3 configuration and even threw in an XP desktop fully set up. He was, however, a bit evasive on the origin of the c omponents. He is a serious mold maker, has two similar machines in his own shop with the same parts as mine, but he uses a Bridgeport for brass.
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On Saturday, February 14, 2015 at 7:08:42 AM UTC-5, robobass wrote in rec.c rafts.metalworking:

one

Not to change the subject, but I've noticed that with amateur phone repairm en/salesmen. I was running around trying to get my phone working again BEF ORE I thought of typing in the symptoms that the phone was having into a se arch engine. All I heard was "go see someone else" or something similar or buy a new phone.
So, when I finally typed my phone's trouble into a search engine: I noticed on various website discussions that others were having the same difficulty with the same model and I tried their solutions and it worked.
Sometimes, DIY is better than what's out there.
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On Saturday, February 14, 2015 at 5:24:21 PM UTC+1, snipped-for-privacy@hotmail.com wrot e:

.crafts.metalworking:

r one

rmen/salesmen. I was running around trying to get my phone working again B EFORE I thought of typing in the symptoms that the phone was having into a search engine. All I heard was "go see someone else" or something similar or buy a new phone.

ed on various website discussions that others were having the same difficul ty with the same model and I tried their solutions and it worked.

I have been searching the google, but haven't found anything specific enoug h. Sorry if I'm boring you, but isn't this a nice break from all the ATF st uff?
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I just ordered two 6mm carbide cutters. Maybe I'll try grinding the flutes on one of them. I did notice that my 3mm carbide mill cuts brass with way l ess effort than the HSS Co. Maybe the combination of carbide and a larger r adius will be enough. Two finishing passes too? I don't need a mirror finis h, but it's gotta be better than it is now! Thanks everyone.
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On Sat, 14 Feb 2015 04:15:43 -0800 (PST), robobass

Something is funny there. There should be little or no difference in the "effort" required by a carbide cutter versus HSS. If anything, the HSS should require slightly less effort, given equal sharpness.
The only reason to go with carbide when cutting brass is if you're burning your HSS cutters. This is extremely unlikely.
There is one other potential issue, however: Carbide is stiffer. If the flexibility of the cutter itself is contributing to the chatter, carbide could help.
--
Ed Huntress

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The tool has 22mm of 4mm length, so I'm thinking deflection is a suspect, a nd a shorter (and carbide) tool should help. As far as carbide vs. HSSE, so far I've noticed that it plunges with much less strain, but I haven't used it enough for profiling to draw a conclusion.
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On Sat, 14 Feb 2015 08:40:19 -0800 (PST), robobass

There are several things that could be going on here, and I don't like to speculate too much -- especialy from a still photo -- but here are a couple of thoughts that may help.
First, if there's a difference in plunging with carbide versus HSS, it's due to geometry or edge sharpness, not the tool material. It's difficult to make any carbide as sharp as HSS but the carbide may be sharper to begin with.
Second, 22 mm extension on a 4 mm cutter is indeed an invitation to deflection and initiating vibration. Carbide is much stiffer.
Third, the machine configuration looks like an invitation to sympathetic vibrations; changing speeds could help deal with any oscillations. Have you tried slowing it down? That's why they build machine tools from cast iron. It doesn't like to vibrate. <g>
Regarding dubbing, radiusing, or back-chamferring the cutting edge: it could solve any digging-in, to which brass is very prone; or, by increasing the cutting force, a radiused or negative-chamferred edge could make things worse, by increasing tool deflection.
Chatter can be difficult to track down. Good luck.
--
Ed Huntress

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On Saturday, February 14, 2015 at 6:03:26 PM UTC+1, Ed Huntress wrote:

, and a shorter (and carbide) tool should help. As far as carbide vs. HSSE, so far I've noticed that it plunges with much less strain, but I haven't u sed it enough for profiling to draw a conclusion.

"the machine configuration looks like an invitation to sympathetic vibrations" Yeah. That too. The table definitely moves around alot, so I'm at the momen t working on securing it to the brick walls.
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On 2/14/2015 6:23 AM, Ed Huntress wrote:

Right and if the cutter is a 4 flute, there isn't time for cuttings to clear before the next tooth comes and that might be the jitter. Turn slower and move slower and see if the roughness goes away.
HSS really HSS not 'cheap steel' cutters would be far above a match and can have a sharp edge to shave off the brass cleanly.
The nose on carbide is rounded as carbide shatters easily if pointed.
I use carbide on Bronze and HSS on brass. I mill and turn both.
Another issue might be to deep of a slot being cut. Hogging out to much metal in a pass.
Martin
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Update. I did a bunch of things. Got a beefier vise, added more fasteners o n the table, reduced the finishing pass width, depth and feedrate, and went with a thicker and shorter carbide mill (instead of HSS-Co) for the finish . Result is Super. You would never know I did the work on a gantry router i nstead of a knee mill!
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On Tue, 24 Feb 2015 07:40:57 -0800 (PST), robobass
Great news! You'll never know which change(s) did it, but it's still good.
--
Ed Huntress

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"I think you mean your spindle axis(Z)is not perpendicular to the XY plane (your table), right?"
Yes. I made sure the spindle was perpendicular to the carriage, but the ent ire transport assembly appears to not be fully aligned to the table base. T he only way I can see to adjust it is with shims, or to face the whole tabl e.
Here is the machine:
http://s1262.photobucket.com/user/Modelbauer1963/slideshow/CNC2
If you look at the first photo, you see that the table seems to dip toward the lower left. It could also be that I just mounted the work poorly, among other things. The quick fix is to simply face the plastic block before the next run. Something I should have done first, but the block itself seemed pretty good.
"Do you have a link to the CNC machine you own?"
No. It seems to be hand built by the seller. There is "RT Technik" engraved on the front, but I found no web hits. Few of the components even have lab els, but the seller says he got everything locally, and to contact him if I need any parts. Here in Germany there are maybe a dozen commercial manufac turers building machines like this, as well as many individuals making them in their garages and selling them on Ebay. I shopped for a year and this i s what I chose. So far it seems like I did well. Much of the Mach3 controll er software is still a mystery to me, but fortunately the seller walked me through the basics. The hardest part has been creating decent toolpaths usi ng Bobcad26. I'm not sure that was a good decision, but I am getting the jo b done now, after like two months of despair.
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Update. So after all of the tweaks, I think that going with a 6mm 4-flute c arbide mill was the biggest single thing. I first rough a thru-slot with a 4mm mill to reduce the stress on the larger mill as well as allow chip clea rance. Here you see just the roughing pass. 0.5mm cut depth per pass, and l eaving 0.05mm for a full depth finishing pass. If you remember, I'm doing t his with a gantry router. Works well enough!
http://i1262.photobucket.com/albums/ii619/Modelbauer1963/CNC2/SlotFix1.jpg
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