Milling with the Hobbymat

[Roger B]

It is many years (decades) since I used a ‘normal’ milling machine. All my work has been carried out with a vertical slide or a combination lathe and milling head.

I needed to mill a piece of 6mm wide EN8 as part of my current project. I used a 16mm end mill running at 365 rpm (lowest available) with a 0.5mm depth of cut and a feed rate (by hand) that felt comfortable.

<a href="https://www.youtube.com/watch?v=weLhTMHnhhw" target="_blank">http://www.youtube.com/watch?v=weLhTMHnhhw</a>

Does this look and sound reasonable compared to a proper milling machine? There is visible movement of the compound slide. The finish is OK for the purpose and can be cleaned up a little with a file if required.

[Zephyrin]

I would say that it's not very fast...on the flimsy equipment that I have, I would prefer faster rotation and slow advance.
On a slightly weak mount, I'm afraid that the large cutter, especially with few teeth (2, 3, or 4), will engage with the workpiece and ruin it if the rotation is slow compared to the feed rate...
But why use a 16 mm cutter for a 6 mm workpiece? Simply because the cutter is already mounted?

[Charles Lamont]

The cutting speed of 60 ft /min sounds about right to me for EN8.

I agree the cutter length means things are not as rigid as with a shorter one.

It sounds to me as though the end mill may not be all that sharp.

I would not machine steel with an HSS cutter without using some cutting fluid. 

[john mills]

the years when i was using milling machines all the time i often run that size end mill at about that speed
it was usually tool steels but that speed will give reasonably good tool life  for light machines why run faster and have a short tool life with a relative feed looks good to me
john

[Jasonb]

Sharpness of the cutter would be the first thing I would look at. If you have been using it previously with the vertical slide taking the same shallow 0.5mm cuts then the end is likely to be worn.

As mentioned above a smaller dia cutter so that you always have at least one flute engaged, preferably 2 will also help with the bonus of keeping the gearbox noise down.

Smaller cutter for the smaller width cut also works out more economical as an 8mm is likely to wear at the same rate as a 16mm but the 8 is a lot less expensive. It is also quicker as for the same chip load you can feed faster due to the higher spindle speed that can be used with the smaller cutter while still keeping the cutting speed the same.

[Chipswitheverything]

I would agree with people's above comments about lack of sharpness of the cutter at the extreme business end : the tip sharpness is lost pretty quickly in use. And I would think that sloshing with cutting oil, probably of a straight variety on EN8 , but soluble would help too, would be absolutely necessary for a better finish.
Milling is a very vibration prone sort of job, and a very light machine with the cutter extended some distance from the spindle nose will have its limitations in combating it. Mostly, when I can,  I use simple home-made cutter holders that tuck a smaller diameter end mill, 8 or 10 mill or equivalent, up into the taper of the spindle for the best rigidity.
  If the side flute cutting edges are in sharp condition, then turning the head and arranging the workpiece to use them could be beneficial, - though admittedly, hardly worth it for a one off job that, as you say, can be cleaned up. Dave

[vtsteam]

Keeping HSS end mills sharp needn't be expensive or require a complex cutter grinder. (Though they are wonderful if you have one) I made a sharpening jig for a small damaged 5" disk sander that does a great job on the ends of the flutes. Grinding the side flutes is another matter, but most of the time, for me, it's just the ends that need a touch-up.

[crueby]

Vtsteam - interesting jig!  Do you tilt the table slightly to give the cutting edge a relief angle?

[vtsteam]

Yes, Chris. also that slide you see has an angle built into it as well, it's not 90 degrees to the disk. So it's a compound angle

I don't remember the angles I used, it's been a few years, and it retains it's setup, so I haven't changed it, but I can look it up.

If interested I can do a write up on making it in the tools section.

I also can use it to similarly set the compound grinding angles on a lathe tool for things like say, making an acme threading tool (which I have done).

Another point in its favor -- we're told not to grind on the side of a grinding wheel for safety reasons, but the front leaves a concave grind. But a disk sander has no such problem. And the grit can be easily renewed with a new disk.

[internal_fire]

How well can you sharpen to the same depth on each tooth? I do not see any sort of axial stop in your photos.

I have tried similar things and always end up with one tooth doing all the work.

I have a wheel that is specifically designed for side cutting. I don't work it hard of course. The heavier cutting is done on the periphery.

Gene

[vtsteam]

I've had good luck doing it by eye. You could rig a stop if needed. I also sharpen my big drills by eye and gauge. (not with this rig, but a grinder).

[Jasonb]

Unless you are only taking very shallow cuts it is unlikely that one flute will be doing all the work.

Assuming the cutter is moving sideways then it is the sides that do the cutting so for example if doing a 1mm cut and you had 0.25mm difference in lengths you would still have all four flutes doing 75% of the cutting, 2mm depth of cut and you are then getting 88% etc.

With the low cost of small carbide cutters these days I don't bother to sharpen.

[internal_fire]

Unless you are only taking very shallow cuts it is unlikely that one flute will be doing all the work.

OK, that was an exaggeration. However, the surface pattern is definitely rougher when the teeth are not even. It takes only a very small difference to be seen on a finished surface.

Gene

[Roger B]

Thank you all for your inputs   
 
It sounds like I am not doing too badly 

Some more details/explanations:

I used the side of the milling cutter to face the ends of the rack, the results were similar.

The cutter was one of a set from CTC, so not the highest quality but OK. I have read in a couple of places that it is better to use a cutter wider than the job in this situation and also that it should be offset. This may be more relevant in ‘industrial’ use.

I do use a cutting lubricant from an aerosol can which I spray lightly on the surface to be cut before I start. This particular one is quite expensive but odour free which is essential for use in a shared cellar 

[Jasonb]

Looking at the swarf on and behind that cutter I would still say it is past it's best.

A sharp cutter will produce clean long chips the full length of the workpiece being cut and leave a minimal burr