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skipd1
04-23-2012, 05:13 PM
About a month ago I purchased a used Clausing 8420 mill in fairly good shape. It came with some tooling and a decent vise. Finally after getting it cleaned up and set up to cut accurately I first set up to edge a piece of 1/4" X 3 1\2" mild steel and then layed it in the vise on a couple of parallels so it was a little proud of the vice jaws. I installed a cheap 1/2" 2 flute endmill in a MT2 colet and started to take off passes about .010 deep making about 8 somewhat overlaying passes.
I am quite pleased with the accuracy and flattness of the cut, but the finish is a little rough or would you say furry??. Anyway do I need to use a better or higher flute (4flute) mill, or make more overlapping passes or both? I don't have any power feed on any of the axes yet, so I went resonably slow feeding the mill into the work. I did not make any finnishing passes with the exception or returning the end mill back over the cut to start the next. I also noticed I need to get a small plexiglass shield as there are a lot more little flakes flying off than cutting on a lathe!
Thanks
Regards.
Skipd1

Clevelander
04-23-2012, 08:01 PM
For cutting steel the 4 flute will give you a better cut. For aluminum you need to use a two flute with a high helix a climb milling to prevent "welding' of the swarf back to the parent material.

Generally, in my experience, milling does not tend to provide a very smooth finish (of course the issue of smooth is a totally relative thing). In my (so far, under educated experience) a light cut with a fly cutter seems to give the best overall finish. That said to a great extent the proper shape of the cutter tool in the flycutter will greatly influence the smoothness of the finish, that is a slightly rounded cutter will tend to give a smoother finish than a pointed tool as it "cleans up after itself" as it goes through the cut.

The smoothness of your cut will also have a lot to do with the cutter quality, shape, stiffness of the frame of your mill, the trueness of the spindle, the quality of your bearings, the grade of the steel (damn, I'm starting to think if it's cloudy or not it affects it ;) ).

I wait for feedback from the more experience people.

Dr Stan
04-23-2012, 08:29 PM
(damn, I'm starting to think if it's cloudy or not it affects it ;) ).

That and how you're holding your tongue :D

It sounds like the OP was thinning the piece of CRS, so a fly cutter would be the best option for this type of operation. Something like these:

http://www.travers.com/skulist.asp?r=s&n=||UserSearch1%3Dfly+cutters&q=block+id+119081+and+class+level3+id+30252

Davo J
04-23-2012, 11:37 PM
You should be getting a nice smooth surface, but it will have visual marks in it from the end mill that could be measured with the right gear, but that is usually good enough for most jobs.
If you surface is rough, check your speed and feed and also the end mill. A new quality end mill will leave a nice smooth finish, but you will still get the circular marks.

Like the other guys said a fly cutter will do a good job. and also a face mill.
With the fly cutter/face mill, if you have the mill head trammed spot on it will leave a criss cross pattern on the work as both sides of the cutter touch the work as it passes over the job. You can have the tram out slightly and the cutter will only leave marks in one direction. This is fine just for looks, but the surface will actually be concaved slightly, so no good for mating parts.

If your going to be using HSS, I would recommend using coolant as it will make you cutters last a lot long. It not only keeps it cool, but also washes away the chips so they don't get recut which is extra wear and can also mess up the surface finish. A simple pond pump can be used for the coolant pump.

With carbide I just run it dry because of the speed they do it sprays coolant everywhere.

Dave

Mcgyver
04-24-2012, 10:46 AM
mild steel just doesn't leave a great finish with whats available in the home shop. When you see it with a mirror finish its off some 1/2 million dollar super rigid mill with a 25 hp spindle, not a used bport style light mill.

First thing is make sure it is a sharp cutter run at or under its recomended max speed.

I agree a fly cutter would be better for this job and also suggest coolant. I use flood most of the time. best finish will be a very sharp cutter (think like mirror surfaces the way a quality woodworker goes at a chisel), big radius run as slow as you can go, light cut (couple of thou) and dark cutting oil.

someone mentioned climb milling, not on that machine unless its a very light cut

Basically, filing, emery paper or a surface grinding are how to get good finishes on mild steel. flycutting can be ok. I'll often do quick power scrape because I like the look.

darryl
04-24-2012, 03:12 PM
You also have to take care when clamping the piece in the vise. One general procedure is to keep tapping the piece into place on the parallels or shims as you tighten the vise. This keeps the piece bottomed as it gets tightly gripped- otherwise it will often rise up a bit as the jaws wedge.

dian
04-24-2012, 04:05 PM
how do you climb mill when facing?

Jaakko Fagerlund
04-24-2012, 05:01 PM
mild steel just doesn't leave a great finish with whats available in the home shop. When you see it with a mirror finish its off some 1/2 million dollar super rigid mill with a 25 hp spindle, not a used bport style light mill.
Nah, the most usual reason is not enough surface speed. I have noticed that a regular steel (S355, Fe52, whatever you want to call it) gives a very nice finish if you get 160-200 m/min cutting speed at least. This just doesn't happen with a lathe in small diameters as usually the top speeds are around 1000-2000 rpm and thus would quite big diameter to get that speed.

Clevelander
04-24-2012, 07:15 PM
I got on my micro mill today to make a cross slide assmebly for the small small lathe that I'm building. I haven't used the machine much and I wasn't all that keen on how the cross slides were working plus I was having a hard time getting a non tapered piece of material when I faced parts. I thought I'd cleaned the parts when I first got the mill but I did a tear down on the whole cross slide assmblies today.....gotta love hind sight. Damned if I didn't find the anti rust coating smeared on the ways and the gib screws so tight that you'd never know if it was the gib or the screw that was tight. I chased the threads, washed everything, lubricated everything and indicated my vise to make sure everything was square and the slop was out of the ways. The only fly in the ointment was that try as I might I couldn't get the material to sit flat in the vise (I indicated the jaw and it was true) the only thing I can think is that the moving jaw is jacking up when I tigten it. I finally put a small piece of card stock at the top of the fixed jaw and suddenly the world was my oyster. I really went the whole distance, I even put the endmill in as far as it would go to reduce flexing. I am pleased to say that I got the best finish I've ever had on the mill (it's 6061 that I'm miling) the finish actually glows.Even on this machine I was doing climb milling. A couple of things are important if you're doing this: relatively light cuts and enough drag on the gib strip so the feed screw has to move the table, if it's too loose the endmill can feed the backlash on it's own....not a good thing.

In regard to the question on climb millng if you are facing with a flycutter and doing the entire face it of course becomes moot. but if you have to make more than one cut it's done so the swarf comes off the cut and is ejected off the side of the material rather than pasting it back into the material that you're cutting.

A couple of things I'll mention, in regard to the CRS. You may want to check the surface after you're done to make sure the material hasn't bowed from internal stresses. When you mill off a single face without stress relieving the material apparently it can make it bend.

The other thing that I think may help you with the" furries" is to use an endmill with a small radius on the corners, the sharp corner on your endmill may be contributing to the problem. Like putting a small radius on your lathe tools enhances the finish.

Clevelander
04-24-2012, 07:18 PM
I have not as yet used a face mill, I imagine that the ones that take inserts are pretty expensive to feed but I was wondering about the quality of the face finish as compared to a fly cutter. Who's got feedback on this in terms of cutting speed and finish by comparison?

Thanks.

skipd1
04-25-2012, 09:55 AM
You guys are amazing and I want to thank everyone for their input. Great info and lots of good info for me. I will try many of the suggestions and let you know how it changes the quality. Also I have some inserts comming for a small 2" sandvik face mill that I will try. I'll let everyone know how this small face mill works on a small mill like the Clausing 8420.

Regards
Skipd1

Davo J
04-25-2012, 10:08 AM
I have not as yet used a face mill, I imagine that the ones that take inserts are pretty expensive to feed but I was wondering about the quality of the face finish as compared to a fly cutter. Who's got feedback on this in terms of cutting speed and finish by comparison?

Thanks.

Face mills with a positive rake leave a pretty good finish in mild steel, but I think the fly cutter leaves a better finish. As for time the face mill wins hands down. Also once the inserts get a little wear they start to leave a porer finish.

Dave
Edit
I have a 63mm face mill here from CTC tools in china and it only cost around $140 with 10 positive rake inserts posted to my door, so not a bad price and it works good.

Davo J
04-25-2012, 10:12 AM
You guys are amazing and I want to thank everyone for their input. Great info and lots of good info for me. I will try many of the suggestions and let you know how it changes the quality. Also I have some inserts comming for a small 2" sandvik face mill that I will try. I'll let everyone know how this small face mill works on a small mill like the Clausing 8420.

Regards
Skipd1

That Sandvik face mill sounds nice, they make some good gear.

Dave

Mcgyver
04-25-2012, 10:36 AM
Nah, the most usual reason is not enough surface speed. I have noticed that a regular steel (S355, Fe52, whatever you want to call it) gives a very nice finish if you get 160-200 m/min cutting speed at least. This just doesn't happen with a lathe in small diameters as usually the top speeds are around 1000-2000 rpm and thus would quite big diameter to get that speed.

right, but running a 4" dia carbide face mill at those speeds and taking a decent doc and feed isn't something you're doing on a light machine.....which is where the big hp and big rigidity come from

Generally, the home shop default position, at least imo, is hss where possible. 1) lower total disbursements is more important than through-put. and 2) On these light mills you can very easily reach the machines removal rate with hss so whatever removal rate advantages carbide might is moot.

dian
04-25-2012, 02:40 PM
"In regard to the question on climb millng if you are facing with a flycutter and doing the entire face it of course becomes moot. but if you have to make more than one cut it's done so the swarf comes off the cut and is ejected off the side of the material rather than pasting it back into the material that you're cutting."

so does this mean you only mill in one direction and somehow move the cutter back around the workpiece? incredible, do people really do this? i have never noticed a diffeence in surface quality between back and forth passes.

Mcgyver
04-25-2012, 03:17 PM
"so does this mean you only mill in one direction and somehow move the cutter back around the workpiece? incredible, do people really do this? i have never noticed a diffeence in surface quality between back and forth passes.

you would have to frame it in a specific circumstance, but often yes, but not really with fly cutting. Fly cutting, usually a light cut, doesn't much matter in terms of climb, but, you should orienting the cutter to enter the work at a tangent to reduce hammering....so that pretty much means you're not climb milling.

Climbing milling is an issue when the cut is heavier in which case you just can't do it unless the mill is set up for it - ie anti backlash. If I'm using the horizontal, or on the vertical if you're say taking 1/2 DOC, 1/2" width of cut (say, making a shoulder), there is just no way you would climb mill this (on a regular b port style). If you have to do several passes, to get it do say 1.5" depth , yes, you would crank the work back to start each pass so it was not climb milling. You might climb mill a finish pass at the end, but can't say this is a huge advantage to it vs regular milling with flood, sharp cutter and slow feed..

I tend to go full dept of cut if possible, flood coolant and then lower rpm and feed to keep things within the mill's removal rate capabilities. It just makes no sense to do 20 20 thou passes, instead do one at 400 thou. The slowing cutting speed prolongs cutter life, and using more of the cutter is preferable than to concentrating wear just on its end.....all this means trying for heavier cuts where climb is a no-no.

Without backlash eliminators, climb milling can cause a crash if the force exerted by the cutter is enough to overcome the table's inertia; machine either needs to be able to handle it or cut kept very light - ie a final finish cut.