slot cutting in brass

[condeesteso]

Any advice please? I need to cut slots in brass sheet 2mm or maybe 3mm. The slots are round ends, about 70mm long and 9mm across (diameter of cutter). I don't have a mill of course. I do have a pillar drill, various routers, an ML7 but no mill attachment. I may need to do a few and hand-cut is very tedious!

p.s. 8mm would do, I think 9mm cutter may be hard to find.

 

[chipmunk]

Hi Douglas,
9mm milling cutters are easy and cheap to get hold of see...
http://www.arceurotrade.co.uk/Catalogue/Cutting-Tools/Milling-Cutters/HSS-End-Mills
...and I'd use your ML7 without a doubt if your brass sheet will fit on the cross-slide.

You need to make sure the cutters run true to get them to cut on-size (4-jaw chuck in your ML-7 ideally if your 3-jaw doesn't run true and you have no collets).

You don't really need a milling slide but you may need to knock-up something in its place. How about a block of wood to which you can G-clamp your brass? FYI M8 roofing bolts with the heads filed narrower and shallower will fit in place of tee-bolts into the T-slots of your cross-slide.

You can arrange for these to pass up through your wood and then fit washers and nuts on top of the block.

Orient the brass so that the slots to be cut will be horizontal and so that the cross-slide can progress the cut. Engage the half-nuts and turn either the Simmonds nut on the RH end of the leadscrew to position the brass (assuming you don't have a hand-wheel) or buy a cheap hand-wheel (http://chronos.ltd.uk/acatalog/Myford_Lathe_Compatible_Acessories.html) or turn the leadscrew with the gear on the left-hand end.

I hope that's clear
Jon

 

[Inspector]

According to a machining app I have, brass can be cut with uncoated carbide at 800 surface feet per minute. An 8mm end mill (0.320") at 10,000 rpm is a touch above that. If it were me and the brass was large enough to somehow clamp solidly, I would try to "mortise" it with a router and guide bushing, speed dialled back to the lowest rpm, using the carbide end mill with some grease or wax smeared on the brass for lubricant. Bacon fat would probably do but could attract unwanted visitors. (homer) Don't force the bit and protect against the hot chips. A carbide router bit for mortising wood might also work for a few slots. Chipmunk's link also has the uncoated 8 mm carbide bits.

Pete

 

[condeesteso]

Many thankls for all this, quick service too =D>
On balance I think I like the ML7 option as it feels more controlled. My chuck is a 3 jaw, but I'll check concentricity. If I am doing a few of these I guess a collet mounted into a Morse taper into drive spindle would be best? (Sorry if terminology isn't right). Those cutters are worth a go at that price, and on brass should be OK.
I shall give this a go and report back, many thanks all.

 

[Jamesc]

+1 for the ML7

Brass has a nasty habit of snatching. The further you can keep your digits away from the cutting area the better.

James

 

[Cheshirechappie]

Just a small tip - brass has a reputation for being very 'grabby' to machine - it tends to pull the cutter from it's holder into the job. This is especially a problem when the cutter is only held in a 3-jaw chuck or drillchuck - failure is almost assured this way! At best, that could mean the depth of cut increasing during a traverse, at worst it can lead to broken cutters or workpiece wrenched free.

Two ways to avoid this. The first is by using a proper milling chuck (Clarkson or similar) to hold the slotdrill (a better bet for a job like this than an endmill). The type of chuck should ideally have collets which screw onto the cutter, and a cap to fix the collet into the chuck body. Make sure the cutter is screwed right home to the locator point at the inboard end before nipping up the cap. Also - very important - hold the chuck into the machine spindle with a drawbar. An ER-type collet with full length grip on the cutter would probably be OK, too. The second way is to grind or stone a flat on each cutting lip of the cutter, so that it presents a zero rake to the workpiece (this dodge works well with twist drills in brass). This flat needs to a bit longer than the maximum depth of cut envisaged.

 

[chipmunk]

The points about the grabbiness of brass are well made but some of this can be helped by taking lighter cuts.

You could try one of these with an M10 draw-bar through the headstock of your ML7... http://www.arceurotrade.co.uk/Catalogue/Cutting-Tools/Milling-Cutters/End-Mill-Holders

Extend the cutter as far as possible before tightening grub screw to prevent cutter being pulled out during the cut.

HTH
Jon

 

[woodpig]

As Mr Chappie days, you should really be using a slot drill rather than an end mill. I'd still chain drill a little underside first though.

 

[chipmunk]

Hmmm, the cheap end-mills I linked to are centre cutting ones.

So, I'm not entirely convinced of the advantage of a slot-drill (- presumably 2-flute?) here.

...anyway I'd also argue that this is a bit of a moot point these days - see for example here... http://www.model-engineer.co.uk/forums/postings.asp?th=69104

Jon

 

[woodpig]

The subject of slot drill v end mill has been done to death on many engineering forums. Mostly because few of our American cousins know what a slot drill is or what it's for. The clue of course is in the name.

Post number three here explains it nicely:
http://www.modelenginemaker.com/index.php?topic=4518.0

I struggled in the past to get decent quality closed slots even in alloy because I wrongly assumed I'd get a better cut with more flutes. Using the correct tool I now get nice slots (most of the time :wink and to the expected size!

 

[rxh]

Douglas,
If you don't think that the number of slots to be made justifies obtaining new tooling you could make them by drilling holes of the right size at the ends of the intended slot, scribe between the holes to mark the edges of the slot, cut out the waste just inside the lines using a powered fretsaw (scrollsaw) then clean up to the lines using files. I have cut brass up to 1/4" thick this way, with a thin sheet of wood or expanded polystyrene under the brass to prevent it from catching on the table and using a little thin oil to lubricate the cut.

 

[condeesteso]

Plenty of good info here, thanks all. I've read all the links re slot drills / end mills. The original link is 4 flute 'end mills' but centre cutting. I may need to invest in collets etc, but I think this is worth a go anyway. Given the tendency to grab, is it worth drilling a through clearance one end of slot and allow cutter to remove stock cutting on its edges, maybe? Or otherwise take very shallow cuts and plwnty of passes. I'll assume rock-solid fixing of workpiece also.
Sorry RX, re obtaining new tooling, I don't have a fretsaw (but I know a man who does, and abloke with a mill, and a cnc mill...). My idea, so my problem :lol:

 

[-Matt-]

I'd be making up a cutting jig and reaching for the plasma cutter...
Or maybe look into the possibility of getting it laser/water jet cut if theres alot of them to do?

 

[AndyT]

How many are you making Douglas?
All you need is a jeweller's piercing saw, a few blades and a small drill bit.
Thin brass of only a millimetre or two is quick and easy to cut, without the need for colletts, milling cutters and experiments in setting it all up.

 

[condeesteso]

Probably 6 Andy, but maybe 12 :wink: I did a prototype that way in 1.6mm (which was too thin anyway) and it was rather slow and faffy, ended up slightly unperfect. As I have the Myford, I can mount the stock cut to size onto the cross slide and see how I go with a cutter in the chuck or get a collet/mount. If I can do all six exactly the same and looking good that's the aim, these things will be on show so need to be nice. By the way, overall dimns are 30 x 95mm (approx) with slot down centre 9mm x 65 approx. And I may need to go to 3mm so a repeatable process would be good.

 

[woodpig]

I'd try mounting the cutter in a three jaw chuck first, I've done this lots of times without issue. If you can mount the work securely you could probably cut three plates at a time. As said before I'd remove most of the material first by chain drilling then cut out what remains with a slot drill. I've got a milling machine but I still sometimes chain drill thick materials before milling. It will also be easier if you set up stops for the cross slide. I always use stops on the table of my mill when cutting closed slots.