Face mill or fly cutter for cleaning up sheet stock?

[Tait]

Hi all,

I want to get the residual scale off CPM steel that has been debarked but still has the brownish-grey stuff in pits up to maybe 6 thou deep. I've read and read and looked and looked. I don't have the room for a surface grinder.

My intent is to make folding knives. YES, I know many people claim you need a surface grinder for folders. I know several makers who don't have one.

As far as I can tell, my best option will be to clean it up on my mill/drill (a Weiss WMD30LV).

Options for cleanup would be:

1) flared cup wheel as a grinder (works great according to Jim Moyer; his mill has covered ways, mine does not! eek!)
2) fly cutter
3) face mill

I have a fly cutter and find it's a pain to crank slowly and steady enough to get a smooth surface. I'd be interested in thoughts on face mills for cleaning mill scale:

• is this a good idea (guessing yes if I want to pay for it!),
• do I want a 45 degree angled tool, or a 90 degree (guessing 45 for HP requirements),
• what size can my mill likely handle (advertises it can take a 3" face mill!?!)
• how deep a cut to plan on taking (guessing a few thou, say 5, would be a reasonable start point, so probably have to take 2 passes),

 

[richard j]

i sent you a pm. i have some other optioins that are too long to list.

 

[AcridSaint]

The biggest problem with the fly cutter is that you're going to dull it very quickly with mill scale.

Instead of maintaining a slow and steady pace, perhaps take less off and just speed it up a bit.

You may be able to find a place locally to blanchard grind your stock for you and get it close enough. There are a lot of factors to a folder, but at the end of the day, many folders are not built with tolerances that actually warrant PG steel.

 

[Bruce Bump]

A disc grinder is so handy for folders. Fresh coarse grits for the pits and fine paper for the final thickness and finish. I just have a 6" delta and use it but when I grow up I'm getting a variable speed with a 9" from Rob Frink. It helps to cut your parts out before attempting to surface them. Its hard to surface an entire stick of steel. Just my 2 cents.

 

[Tait]

Thanks for the replies so far, good suggestions.

I'd love to do the disc grinder - just the costs add up kind of quick!

 

[Nathan the Machinist]

There are some very useful things you can do with a fly cutter including : external thread milling (for things like buttress or acme threads), o ring grooves, splines in shafts, key seats, and perhaps things like nail nicks in folders and texturing flat scales. You might even could cut a gear with one if pressed. The beauty of the fly cutter is you can custom grind the profile you want into a lathe tool and hey presto. But the most common use is to flatten the top of something, for which I hate the little bastards. They flex, they dull quickly, they hammer when pressed, and they really don't leave a particularly good finish compared to a modern face mill.

And. They. Are. Slow. A decent finish might require 4 IPM or less. A five insert face mill can achieve an equal or better finish at 20 IPM.

And face mills are rigid and use modern milling inserts, so they can often leave a near mirror finish and not dull very quickly. And a modern face mill is quiet and doesn't hammer your spindle.

I don't know if you saw the thread, but I used a couple face mills in the radius platen WIP I did a couple months ago. I hogged many pounds of steel with them and also used them to put a fine finish on the sides of the radius platens. That cut required only a single pass across the sander to remove the tool marks, so the tool marks were very shallow.

So, my vote is for the face mill if you can swing it. For your use a 45 with an octagonal insert (or square insert with flat corners) might be a good bet, but certainly not your only option. And for a low HP machine you're going to want one of the high rake face mills designed for smaller machines. A honed insert designed for aluminum might work well in your application too (very light cut, .005" per pass).

How big? That's a tough one because ideally the face mill is larger than your cut, but you might have problems running a 3" face mill on a small mill. If you're flattening 1 1/2" wide stock, you'll probably want a 2" face mill. I don't have experience using a small machine for face milling but I expect chatter and harmonics are going to be a problem. But whatever you're doing with a fly cutter, the face mill is going to do better.

A problem you'll run into cleaning up the skin on your CPM is it is going to warp a little once you skim it off. That is going to happen if you mill or grind. So you might need to do a cut on one side, flip it and do the other side and go back and forth a few times taking light cuts to keep things flat.

A problem you might run into milling that you don't run into when grinding is the trouble with clamping the steel and holding it perfectly level so you're not cutting more off one end than the other. I recommend doing this in a good machine vise on good parallels and practicing on scrap to be sure you have a good handle on precisely clamping a work piece. Make sure there are no burrs on the steel or crud on the vise or parallels. Depending on your vice, you may need to tap the workpiece down with a small mallet as you clamp on it. Measure your work and see how you're doing.

And finally there is the problem of cost. A good vice and parallels might be $500. And a good small face mill might be another $300, with inserts at $10 a pop. I don't have much experience trying to achieve good accuracy and surface finish with "consumer" grade tooling, so I don't know how much you're going to have to spend to get the results you're wanting.

If, for whatever reason, your face mill isn't putting all the inserts down to the same depth, you can always run a single insert and use it like a fly cutter (on steroids) for the finish cut, as a last resort.

Wow, I've been writing for 20 minutes, I typed a freakin tome here...

Please post what you do and the results you achieve. I think this is a topic others would be interested in.


Oh yeah, edit to add:

Very light cuts can sometimes cause gouging when the chip is too small to fly off the insert and instead sticks to the edge and rides around for another trip across the work piece, leaving a mark. Sometime you need to take a somewhat heavier cut to achieve a good finish. The use of a cutting oil might reduce this.

 

[Tait]

Wow, that's quite a response - thanks!

Somehow I missed the WIP on the radius platens - nice writeup. (For those who missed it, look here).

I was looking at the Glacern 2" facemill R8-FM45-200 - seems pricey, but may be designed for this use(?): "The R8-FM45-200 is ideal for low horsepower and benchtop machines. Two of the insert pockets can be left empty for minimal power consumption."

I was a little worried about the $10 inserts. How often do you have to re-index? Would it help to soak the steel in vinegar or whatever before milling?

I have a Glacern vice, and cheap parallels. However, I'm wanting to work stock supplied at .075-.085, so I doubt I can comfortably put that in a vice, and bowing will be a problem. Would that mean I'm also saving up for a magnetic chuck, or would you consider milling a shoulder into some soft jaws?

Thanks again for the replies thus far!

 

[Kevin Wilkins]

What you're trying to do is a grinding operation not a milling operation. Trying to mill stock that thin will put all kinds of stress in the material - even if you screw it down on a plate fixture. Do yourself a favor and send the stock out to a grinding company and have it ground equally from both sides to thickness you want. In the end, you'll save time and money.

 

[Nathan the Machinist]

In my opinion, that face mill looks perfect. You are correct, scale will dull the fine edge you're going to need, so vinegar soak and a wire wheel will help. And lastly, while I have done what you're trying to do on 1/8" stock, I'm not so sure it would work out so well on 1/16". Remember, 1/16" is eight times more flexible than 1/8". I think it will bow no matter how you try to hold it short of a magnetic table. And for all that you might just get a surface grinder.

Kevin is probably right. For the money you're going to spend trying to do this, and not knowing if it is going to work, you might end up time and money ahead just sending it out.