Milling Metals With a Router

[RWoody]

After a little delay, and kindly been directed to the metalworking section by Charley (I hadn't noticed there was one, to be honest ) I'm now putting out a request for some expertise on the subject of milling using a router. I have already discussed this a little on the woodworking part of this site (with some helpful comments I must say) but being a very cautious guy, I'd like to put it out to a wider audience too:

Has, or have, any of you used a router to mill metal with? I'm talking brass in my case. The concerns I have are ones of head rotation speed, as a usual metalworking lathe operates at low rpms in the region of 600, for example, whereas a router, designed primarily for wood, spins at many, many times that, often around the 20,000 rpm mark. While I doubt the router wouldn't cut metal, my main concern is heat. Surely, even if using cutting lubrication (and much would 'spray' off too at these high router bit speeds) things will heat up rapidly, and take off the router bit's temper?

Secondly, because of the fast speed a router has, would not the cutting surfaces become dull quickly too? I mean one isn't going to be able to sharpen a TCT cutter themselves anyway (though correct me if I'm wrong) as they aren't 'soft' like HSS, which can be sharpened, but I'm sure would become dull VERY quickly if milling metal!?

So is there anyone who has first hand experience with this, who'd be able to give a bit of sound advice, please? Thanks in advance. :0)

 

[bugbear]

I've heard of people juu...uust getting away with working aluminium with WW tools, e.g. bandsaw or router, but it's a stop gap.

Brass is well beyond the limit, I suspect.

BugBear

 

[mseries]

I've been reading up on this myself recently, not for brass but for 2mm aluminium. It does seem do able. Heat seems to be the main worry and run your router slower, mine are speed adjustable. I don't have first hand experience (yet) but my mate Aiden said he's done it (Aiden is like Emmet Brown though). I am confident enough to give it a try, I'll make a good jig/holder to hold my workpiece, I am not sure though if I should use my router inverted in my table or clamp the workpiece and move the router. I'm thinking the latter so my cutting fluid/coolant will not run into the router nor will the swarf.

 

[Spindle]

Hi

You need to consider the cutting speed of the tool - see the chart in the link attached:

http://www.littlemachineshop.com/Refere ... Speeds.php

Using these figures a 1/2" diameter carbide tool cutting brass would require a rotational speed of 8,900 rpm - well within the range of a variable speed router.

I wouldn't suggest using a router for deep sections, its just not powerful enough, but for cuts of 2 or 3mm deep in brass and aluminium it should be fine.

Obviously you will need to secure the work well, wear eye and ear protection, traverse the router in a steady and controlled manner and take light cuts.

Regards Mick

 

[RWoody]

Thank you both for this. It kind of confirms my concerns, though not entirely, as it does seem that with very soft metals, such as aluminium, it's possible, at a squeeeeeze! I think I can rule brass out now, it would seem :-(

IF I were to try milling in this fashion I would use my WoodRat, is it'd be ideal for working along in a straight line with good linear and lateral control. It still doesn't get over the 'heat' issue though, in my view; and as you say, there is the issue of ingress of coolant into the bearings of the router, if inverted - quite aside from the 'spray' issue.

 

[Spindle]

Hi

Why would you rule out brass?

Regards Mick

 

[RWoody]

Thanks Spindle, your reply came in while I was typing a response to the other two contributors.

The site in the hyperlink looks interesting, but it only serves to send alarm bells in my head, regarding speed, depth and material etc. So, in light of all I've heard so far, and now you 3 guys, I'm seriously thinking of an alternative material entirely.

You see, what I'm after is a mitre guide, which will fit my rather small guide grooves (as per Mike's excellent review of mitre guides on this website) as the Incra I'm now after has a guide width that's much larger than both of my saw table ones (one is for a circular saw and the other a bandsaw) and EACH of my two machines has a different depth and width guide grooves in the tables. I was therefore originally hoping to make up some metal strips to fit the bottom of the Incra's guide; one for each table. As I have some brass strips, I was hoping to use those. However, I can't see that practically happening now, in light of these information I've gleaned from this forum, which only served to compound my belief that it wasn't really the way to go.

So I'm now wondering about either a very hard wood OR maybe some sort of Bakelite or some other hard man-made material. I can then put some pins upwards in these strips, to engage with the holes I shall drill into the Incra's guide (being careful not to weaken it too much of course). Anyway, I'm sort of gradually coming to an undesrstanding of what I need to to do, and with what material (if I can get hold of it).

Thanks again Spindle.

 

[RWoody]

Hi

Why would you rule out brass?

Regards Mick

I'd rule out brass because it's harder than aluminium; and if it's debatable to even to try with aluminium, then brass will definitely be out. That's all.

 

[mseries]

some sort of Bakelite or some other hard man-made material. .... (if I can get hold of it).

There is lots of acrylic/perspex/plexiglas/lexan as well as phenolic on eBay

 

[RWoody]

some sort of Bakelite or some other hard man-made material. .... (if I can get hold of it).

There is lots of acrylic/perspex/plexiglas/lexan as well as phenolic on eBay

That's true. Funny, but I buy loads of stuff from eBay, so not sure why I believed I had to source it from a specialist. Thanks anyway!

 

[Cheshirechappie]

You see, what I'm after is a mitre guide, which will fit my rather small guide grooves (as per Mike's excellent review of mitre guides on this website) as the Incra I'm now after has a guide width that's much larger than both of my saw table ones (one is for a circular saw and the other a bandsaw) and EACH of my two machines has a different depth and width guide grooves in the tables. I was therefore originally hoping to make up some metal strips to fit the bottom of the Incra's guide; one for each table. As I have some brass strips, I was hoping to use those. However, I can't see that practically happening now, in light of these information I've gleaned from this forum, which only served to compound my belief that it wasn't really the way to go.

The metalworker's way to fit a strip to an existing groove is to file it to fit. Use a turnip file to remove the bulk of the waste, then 'creep up' on a fit with second-cut and finally smooth files. Check frequently with a straightedge and small engineer's square that you're filing straight, and try the fit frequently once you're close. Hold the brass strip in a vice, and use both hands on the file. This will be quicker than you think - brass files easily, especially with a nice sharp new file. Do a 'practice run' with a short strip if you've not tried this before.

Even if you milled the strip to width, you'd have to do the final fitting with files to avoid a sloppy fit. Even on a 'proper' milling machine, getting a smooth sliding fit straight off the machine is pretty unlikely - it'll be close, but either a bit sloppy (fail - scrap) or a bit tight (ease fit with smooth file). [Production guys will get a reasonable fit from the machine, but they'll need a couple of practice runs to refine settings. Better class work is almost always 'fitted' by hand after machining, especially in the case of 'one-offs'.]

 

[wizard]

I would not even think about it the item must be held so there is no movement, milling cutters break very easy, I would not even use a cheap modern milling machine; there are loads of them that have only been used a few times. I have two very old milling machines that work well but you have to know what you are doing.

 

[n0legs]

:?:

 

[jasonB]

Hi

You need to consider the cutting speed of the tool - see the chart in the link attached:

http://www.littlemachineshop.com/Refere ... Speeds.php

Using these figures a 1/2" diameter carbide tool cutting brass would require a rotational speed of 8,900 rpm - well within the range of a variable speed router.

I wouldn't suggest using a router for deep sections, its just not powerful enough, but for cuts of 2 or 3mm deep in brass and aluminium it should be fine.

Obviously you will need to secure the work well, wear eye and ear protection, traverse the router in a steady and controlled manner and take light cuts.

Regards Mick

How do you get 8,900rpm? that's way too fast.

Using the max for milling brass on that table the speed is 200fpm or 2400inches per min. A 1/2" cutter has a circumference of about 1.6" so 2400/1.6 = 1500rpm, definately not within any routers speed range that I can think of.

Also brass is cut dry so not lubrication to worryabout though I would still not do it.

J

 

[SteveW1000]

Aluminium doors and windows have holes for hinges and locks routed, Trend list high speed cutters for this purpose. Brass should be possible with a smaller diameter cutter which would lower the surface speed. What I would question is how you intend to hold the metal while routing it, I'm not sure how this could be done safely.

Regards

Steve

Sent from my ST23i using Tapatalk

 

[Eric The Viking]

I've milled brass very successfully on a router table, using a standard woodwork carbide chamfer cutter (45 degree bevel).

I was converting a straight plumbing spigot into a compression fitting, by machining an accurate 60-degree bevel on the inside edge of the end. I had to accurately tilt the workpiece 15 degrees and work out how to address it properly with the cutter, but it all worked out fine.

It was a while ago, and my memory is a bit hazy, but several things occur to me:

1. Make sure you have enough stock to experiment with.

2. I *think* I used a high speed (flat out on my T11). See speed calc below..

3. I took very gentle passes, that's partly because the result needed to be very precise (otherwise it would leak!), but also I didn't want to stress the cutter nor the workpiece.

4. Think of how a proper lathe or milling machine works: you need a way of advancing the cutter in tiny increments. I strongly suggest some sort of jig, with the ability to micro-advance the workpiece. For example, using an M8 bolt gives you 1mm per revolution (on a standard-pitch metric thread), or M10 does 1.5mm. I used my T11's through-table height adjuster to do this (M10 pitch).

The amount of advance was determined mainly by listening. I couldn't see the cut at all, as it was guarded, so I'd start with it off the workpiece, move it in until just cutting, make a complete pass and back the cutter off again, stop the router and inspect (takes longer to write than to actually do!). The scale on the Trend-supplied box spanner for height adjustment (0.10mm increments) was invaluable: each cut meant the next would start at a different 'depth', so one needed to remember where one got to the previous time.

5. Obviously, this was done 'dry'. Vacuum extraction is essential, as the brass comes off as chips, not turned swarf. These are very sharp-edged, and get everywhere if not immediately contained. You need several soft brushes you're prepared to dispose of AND to make sure the work area is fully degreased to prevent the chips sticking. I was terrified they'd get into the router*, but the airflow from it is upwards, and as far as I can tell nothing got in.

I strongly advise stopping fairly frequently and cleaning up. Don't work on any wooden surface like a bench, as you'll have a terrible time getting rid of the chips that have worked into the surface, and if you don't they'll wreck any finished woodwork that touches the surface later. I used a crevice nozzle on my workshop vacuum to extract as close to the action as physically possible and get a really fast airflow, and deliberately didn't clean the filter after the previous woodwork job (although I did empty it). The brass chips buried themselves in the sawdust on the filter and didn't get to the cloth, or the motor. I blew the filter out after use.

6. When planning the job, think of the clear-up and extraction needed first, and work backwards to the actual cutting process.

7. Be analytical: There are cutting speed tables available for working brass. You can work out the cutting speeds for a given cutter and router setting: say your cutter is 1/2" (say 12.5mm), and the router speed is 20,000 RPM:

20,000 RPM is around 333 revs. per sec.
cutter circumference is PI x 12.5...     = 39.3mm
so           cutter speed is 13,089 mm/sec

You can work this out for whatever cutter you're using and adjust the speed accordingly. If you're cutting at the right speed, it's one less problem to deal with if the results are poor.

8. Vibration is your enemy, too. At the speed I was working, I was essentially thumping the brass 40,000 times per minute. If you can't hold the router and the workpiece rock steady (and advance the cutter or workpiece slowly) don't do it. I wouldn't think about anything hand-held, unless I was able to screw down or really heavily clamp the stock. Even then be prepared for poor results.

I was working on small (1") pipe fittings, so a handheld router was quite undesirable, but I'd still think twice about it for bigger jobs. The router table isn't ideal, as it risks damaging the router internals, but with really strong extraction, it worked for me.
. . .

The results exceeded my expectations. I now have two completely non-standard-size fittings coupling my boiler to the rest of the heating system. I have eliminated two very expensive and _totally_ useless "service valves," after the third pair leaked in the same way as the earlier two. I will never, ever buy that brand of boiler again.

Hope that's not too 'bossy' above. Brass shouldn't need lubrication when it's being milled, so a router can do it pretty well. I've also done aluminium a couple of times, but the results weren't as good.

E.

*like almost all motors, a router's motor coils are enamelled copper wire. Anything that cuts through the enamel has the potential to short out turns of the winding, leading to the motor burning out (end of router, probably). I was taking a big risk in that regard!

 

[Harbo]

I routed the edges of this plane

Using a slow speed on my router table and held freehand.

Rod

 

[Eric The Viking]

I routed the edges of this plane

Using a slow speed on my router table and held freehand.

Rod

Really nice!

I sit corrected on the freehand thing, but did it vibrate a lot and how much finishing did you have to do afterwards?

E.

 

[jasonB]

20,000 RPM is around 333 revs. per sec.
cutter circumference is PI x 12.5... = 39.3mm
so cutter speed is 13,089 mm/sec

Again really is too fast thats something like 2500FPM when suggested speeds for brass are 200FPM!!

 

[Eric The Viking]

20,000 RPM is around 333 revs. per sec.
cutter circumference is PI x 12.5... = 39.3mm
so cutter speed is 13,089 mm/sec

Again really is too fast thats something like 2500FPM when suggested speeds for brass are 200FPM!!

That was rather my point - I can't remember what I used, but you can easily calculate it so you're in the ballpark.