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View Full Version : Milling Finish, Tramming Issue? Vibration?



mattthegamer463
07-18-2016, 12:27 PM
Hi folks, new to the forum, and pretty new to machining myself, and very new to machining on my own without a school shop with machines presumably set up by someone who knew what they were doing.

I picked up a 10 year old Busy Bee B1977 (typical round-column import mill drill) and the surface finish on face-milling is so-so, but I'm trying to figure out what the issue might be. Checking the tram, the X (long) way is about 0.15 thou per inch but the Y (short) is off by about 0.5 thou per inch. However, machining a test block in all four directions the surface finish is indistinguishable to me.

The cut quality was not good, the cutter is used, probably pretty dull, 1/2" HSS 4 flute, and I was probably running it too slow.

http://img.photobucket.com/albums/v321/mattthegamer463/th_20160715_205250.jpg (http://img.photobucket.com/albums/v321/mattthegamer463/20160715_205250.jpg)
(click for big)

I expected that I would not see the trailing cut in one direction, but there are trailing cuts in all directions. Also, it seems to have a pattern of making a trailing cut on and off. This must be caused by vibration, right?

Any tips on what this piece is showing would be helpful, so I can try to resolve it. I'm tracking down some brass 0.001" shim stock so I can shim the column and fix the tram error.

10KPete
07-18-2016, 12:57 PM
Bed moving up and down with rotation of lead screw (loose gibs), quill moving up and down (loose bearings).
Check it all with a 10ths indicator. You'll find it.

Pete

strokersix
07-18-2016, 02:37 PM
Dull cutter and/or lack of lubricant. Built-up-edge accumulates, then breaks off, then accumulates again causing the trailing scrapes to come and go.

BCRider
07-18-2016, 03:32 PM
I also suspect that the buildup on a dull edge has something to do with the skipping.

Also a dull cutter has a lot more axial load so it doesn't cut clean. Instead it lifts the head by some amount which might have resulted in the Y axis tilt being cancelled out by the lift and associated flexing.

Operating the cutter well below the maximum allowable speed listed in tables is fine. Surface finish may suffer if you run crazy slow but at some reasonable RPM which is even down to half or maybe even 1/3 of the RPM for a cutter diameter listed in the tables is fine. And it generally results in a longer edge life for the cutter at the slower speeds.

What is important and under your direct control is the feed rate to obtain the proper chips off the cutter. You don't want to feed so slow that the chips look more like dust. You want to see proper chips even if they are thin and delicate looking chips.

Looking at the picture of the cuts I can see that the leading side is digging deeper than the trailing scuffs by a very inconsistent amount. That may be galling related to material buildup as suggested above. But either way it suggests that it's building up and shedding off only one or two teeth. The trailing cuts are more numerous and closer together. The difference from leading to trailing markings suggests some lean angle as well. And given the use of a known dull cutter might again be due to pressure used to force the cut. When I use a good end mill I almost don't feel the load from the cutter. If you needed to use some significant force to achieve the feed rate for the cut it suggests an overly dull edge. That force can result in the upper setup flexing a little all through the upper gear and could lean the cutter back a little. And that can make the trailing cuts show up more than they should.

The bottom line from all this is that I'd suggest you really can't make any valid conclusions from the cut quality and tramming from using a known dull cutting mill.

PStechPaul
07-18-2016, 03:35 PM
Welcome to HSM! I am also a novice machinist with low-end machine tools and cheap or questionable tooling from eBay odd lots.

Could be the cutter not precisely sharpened on the end, or just dull, as mentioned. A loose spindle could cause the cutter to rock and lose perpendicularity to the work, which would probably leave leading edge marks. They may change depth depending on how hard you are pushing the work into the cutter.

Here are video clips of a similar operation using my HF mill/drill.

http://enginuitysystems.com/files/CAMM111/CAMM111_Vise_Project_1539.AVI ( 84MB - early attempts at hogging with dull 2-flute mill)

http://enginuitysystems.com/files/CAMM111/CAMM111_Vise_Project_1541.AVI ( 40MB - sharper 4-flute mill, heavy cut)

http://enginuitysystems.com/files/CAMM111/CAMM111_Vise_Project_1563.AVI (200MB - lighter facing cut, after hogging on Bridgeport)

http://enginuitysystems.com/files/CAMM111/CAMM111_Vise_Project_1564.AVI ( 40MB - final facing cut)

And the result, before using the surface grinder:

http://enginuitysystems.com/pix/tools/MiniVise_1572.jpg

The marks are not very deep, and I could have cleaned them up by using a better end mill, cutting fluid, higher speed, and lighter DOC.

Joel
07-18-2016, 04:26 PM
Tram it up and adjust the gibs before you bother trying to figure it out further. I used to get shim stock from the hobby store, but automotive feeler gauges and beer cans can work.

As was said, lock your quill and the unused axis, be sure you have a reasonably sharp end mill, and all will likely be fine after tramming and adjusting.

mattthegamer463
07-18-2016, 04:29 PM
Thanks for all the replies. I'm pretty sure there was buildup on one or more of the flutes, definitely wasn't helping anything. Some of my cutters have straight edges and some have a curved edge, where a concave spot is ground out of the leading edge, I'm not sure if those have a specific purpose or not? Maybe some kind of chip-breaker?

I did the test again using a brand new 1/2" 2 flute, 0.015" depth of cut, pretty quick, hoping it wouldn't rub or gall.

http://img.photobucket.com/albums/v321/mattthegamer463/th_20160715_211812.jpg (http://smg.photobucket.com/user/mattthegamer463/media/20160715_211812.jpg.html)

While the tool marks are very visible, they feel smooth to the touch, and just a hint of a change where the different directions overlap. Also, along one edge a long continuous burr was pulled up. I forget if I did this climb or conventional as I was testing both on different sides of the block.

On 10Kpete's suggestion I will take a look at my gibs and see how tight they are. Grizzly's user manual for their almost-identical machine says the gibs are factory set and shouldn't need service for a long time, and this machine never got a lot of use with it's previous owner.

10KPete
07-18-2016, 05:35 PM
That pic tells a good story. Like the other guys pointed out, build up on a dull edge was probably 90% of the issue. As you can
see, any variation can cause an uneven finish.

Pete

BCRider
07-18-2016, 06:07 PM
That second test with the fresh end mill looks a lot better. I'm seeing pretty much the same depth of scratching from the leading and trailing marks and that's what you want to see.

The amounts the head is out of tram according to your first post is something to consider. But in your first post you said that your tram is off by....


Checking the tram, the X (long) way is about 0.15 thou per inch but the Y (short) is off by about 0.5 thou per inch.

The X axis is only 1.5 tenths of a thou off. That's close enough for the girls we take out. And even your half thou per inch isn't at all shabby. For most uses you wouldn't notice that much. And certainly with this being reduced to 1/4 of a thou side on the half inch cut from front to back it's again not going to be seen or felt in the scratching produced by most cutting tools.

Being a touch OCD on this sort of thing if it were me I'd likely loosen the column base screws and stick a .002 or .003 shim under the front edge then torque everything back down and check again. That should take care of the .5 thou/inch tilt.

mattthegamer463
07-19-2016, 09:45 AM
After a couple hours of tightening and loosening the same four bolts, I got the mill to tram pretty close. 0.001" over 5.5" on the X way and 0.0004" over 5.5" on the Y. Put the vise back and did a test cut with the same new 2 flute as before, I'm happy with the results, still quite a bit of burring though, but maybe that's par for the aluminum course.

I also took a good look at the 4 flute that did the bad job in my first post, and as far as I can tell it looks to be reasonably sharp. I do recall chips jamming up on it though, so I guess it was having problems from the clogging. Would using a water/oil "milky" cutting fluid help? I've heard of people using WD40 on aluminum, but that sounds like a good way to make a mess and most people hate on WD40 for most of the "uses" the can claims, any issues with WD and the oil on the machine? I also have Boeshield sprayed on my ways, I assume WD would act as a solvent for the Boeshield coating.

http://img.photobucket.com/albums/v321/mattthegamer463/th_20160718_225238%20Custom.jpg (http://smg.photobucket.com/user/mattthegamer463/media/20160718_225238%20Custom.jpg.html)

I was trying out a vibration-sensor app for my phone to see if it would help identify sources of vibration on the machine, it produced some interesting data
http://img.photobucket.com/albums/v321/mattthegamer463/th_2016_07_19_09.13.53.png (http://smg.photobucket.com/user/mattthegamer463/media/2016_07_19_09.13.53.png.html)

While changing the belts to test different speeds, I noticed the motor-idler belt was getting warm, taking a look I see it's not properly aligned, also it is an "A" belt and not a "B" belt like the manual recommends, so there is excessive contact at the lower parts of the pulley V. Probably isn't helping much. The pulleys don't seem to be misshapen when I take them off the machine, but they are a little frayed and look worn on the contact faces.

http://img.photobucket.com/albums/v321/mattthegamer463/th_20160718_201532%20Custom.jpg (http://smg.photobucket.com/user/mattthegamer463/media/20160718_201532%20Custom.jpg.html)

Looking at this part, the manual shows it is upside down (links because I exceeded the 4 pic max per post)

http://smg.photobucket.com/user/mattthegamer463/media/20160718_201808%20Custom.jpg.html

http://smg.photobucket.com/user/mattthegamer463/media/20160718_201801%20Custom.jpg.html

However the spindle-idler belt is well aligned, so if I take it apart and flip it I may just relocate the misalignment to the other belt.

http://img.photobucket.com/albums/v321/mattthegamer463/th_20160718_202407%20Custom.jpg (http://smg.photobucket.com/user/mattthegamer463/media/20160718_202407%20Custom.jpg.html)

Thanks for the insights, all.

- Matt

10KPete
07-19-2016, 12:37 PM
The use of a little WD40 is almost a requirement when milling aluminum. Or kerosene or any light lube. It doesn't take much,
you don't need so much that it really makes a mess, just enough to stop chip welding.

I apply it with a trigger bottle....

Pete

Paul Alciatore
07-19-2016, 01:27 PM
Whoooah doggie. If your first photo is a four direction test, then I would say your tram is pretty close to begin with. When in perfect tram, the trailing edge of the cutter will slice through the peaks left by that same cutter on the leading edge and you WILL get that double circle pattern in all four feed directions. Once you reach that point, you are splitting thousandths.

You are probably at the point where some additional torque on the column screws will resolve the differences.

For a better finish you can try:
1. A better cutter.
2. Faster spindle speed.
3. Slower horizontal feed rate.

Tip: if you are splitting thousandths, household aluminum foil is about 0.0007" thick and can be used for fine shim stock.

Tip 2: when judging the tram, make sure that the gibs are as tight as possible and are locked down on any axis you are presently not moving. So, lock the Y axis and the spindle feed while making a cut in the X direction and likewise for the Y direction. This is also good advise when making parts too.

BCRider
07-19-2016, 01:32 PM
Is Boeshield a dry film lubricant? Your concern over the use of something like WD suggests that it is. If so I'd suggest you go with a good heavy way oil instead.

The reason being that to be able to move the ways must have SOME play. It's obviously not much once you dial the gybe strip in correctly. After all it's not like the slides are rattling around against each other. But there's still some. Using a heavy body oil fills that gap and produces it's own vibration and motion damping becomes part of the table support.

There's lots of different cutting lubricants that can aid in resisting chip buildup on the edges and which are wise to use. This is The One (http://synlube-mi.com/products/pure-synthetics/universal) that I use. It's a water mixed lube which is very frugal since it is used for general drilling and milling at a 15:1 to 20:1 mix of water to fluid. I bought a gallon about 20 years ago and I'm still working my way thru it. I'm pretty sure I won't live long enough to use it all. I apply the mixed lube from a squeeze bottle that has a 2 inch length of spray can tubing in the end as the applicator. A drop or two that just keeps the cut area and end mill edges wet but not dripping does the job.

mattthegamer463
07-19-2016, 01:54 PM
Boeshield is a "waxy" film that sprays on and leaves waxy finish, I had read it was supposed to be good for mill ways but maybe they were talking about for general rust prevention.

I've been using non-detergent motor oil for general oiling and I do have some water mixed cutting fluid/lubricant that I didn't use in these cases, I'll give it a test. I usually run dry unless its a small cutter in a small hole, or drilling steel, or when using a non-bimetal cheapo hole saw for drilling aluminum sheet/plate under 1/8" thick.

A heavy, sticky oil works well for ways? Won't it gather a lot of chips? I want to make some slip-on covers for the bed and the front portion of the Y way, as it is completely exposed. Perhaps a bellows or a simple rubber curtain like the rear has, better than nothing.

BCRider
07-19-2016, 02:50 PM
Yeah, it does tend to hold the chips. But that's why the ways have wipers or chip shields.

On my lathe I've installed a couple of flexible shields on the cross slide to aid in reducing the amount of swarf that gets on the ways. I used clear heavy gauge vinyl that I had already. So far it's working like a charm.

The new mill has a rubber or plastic sheet guard to keep chips off the ways between the table and column. I'm going to add a clear vinyl sheet guard on the front to do the same thing since there's no wipers on this machine. Of course the X axis ways are underneath so on those it's not an issue.

With the vinyl I just leave it long enough that it overhangs a little. It'll rub the "clean side" against the Y axis hand wheel and my knuckles when I'm turning that wheel but it's smooth enough that it's not a big deal. And it's clear so I can read the graduations through the vinyl until eventually it becomes scarred and yellowed from different things. Then I'll just change it for a new piece or lift it out of the way to read the scales on the hand wheel.

One reason I prefer oil for the ways is the self cleaning that can be done. Pile a bead of oil and run the slide into it and back up. Likely as not there will be some particles in the oil. Wipe away and repeat until you have cleaned away the junk. That won't work with a waxy lube. Also while larger chips might well wipe away smaller "dust" chips will be more likely to embed into the waxy Boeshield film than to be wiped away cleanly. Then they are held in place well enough that it's not unlikely that the slide won't push them out of the way and instead this small dust swarf will be carried under and between the slide and the ways. At least with oil as the lubricant a good wiping will clear the surface of such swarf.

And even during general cleaning it's amazing how the old oil comes away far more dirty than it went on. And I can do this without solvents being needed. So it means I tend to wipe clean and re-oil more often than I would if I had to get really serious about the cleaning which a waxy lube would require.



At least that's my story.....

mattthegamer463
07-20-2016, 11:34 AM
Makes a great deal of sense to me. I'll get that stuff out of there and slather on some oil.