Aluminium Motorcycle tank badges, work holding, bits, feeds and speeds?



Hey all,
Had my Elite Foreman a few months now and so far have managed not to snap a single bit… until this morning!!

All my previous projects have been wood or MDF and this one is aluminium.
I did a test run in MDF just to sanity check the feeds by eye but I think there’s obviously a very significant difference even to the soft metals so rather than risk any more bits getting ‘excalibur’d’ I thought I’d ask here…

I’ve been asked to make some ‘badges’ for want of a better description for the side of a motorcycle tank. My friend is trying to make a replica of a tank that has the company logo embossed from the inside during the process of the tank being made.

I thought aluminium would be a good choice and the machining marks would look cool once laquered in etc.

I figured that the depth of the 3d lettering could be about 2.5mm and could be machined from 3.1mm sheet.

I thought that attaching the sheet (superglue and masking tape) to some sacrificial MDF that could be dissolved away was a good way to hold everything during machining.

I created 3 operations, 3d roughing, 3d finishing and a cut out profile.

The 3d roughing was with a 1/8th 2 flute UC EM and the depth of cut was 1.3mm ramped in 15mm at 80ipm. It made it about those 15mm when it snapped.

(For the 3d finishing and profile I intended to use a 1/16 tip dia 5.4 deg 2 flute tapered BN bit.)

The stock was now scrap anyway, so I thought I’d try an old 3 flute 1/8th UC EM that was a bit stubbier, at .6mm DOC. This didn’t snap, but produced an awful cut with twisted metal everywhere (see pic), then the glue on the tape melted and the stock came off the carrier…

It was at this point I figured I’d seek some advice.

How would y’all approach making something like this from the points of view of work holding, bits, feeds and speeds etc?

The bits I used (and or intended to use) were Spetool and are intended I think only for wood and plastic I think so I figured I might need to buy some metal specific ones.

Any thoughts would be gratefully received!!!

Not all aluminium is the same. I think it’s called Aviation grade Aluminium; I find it cuts nicely, and some non-aviation grade Aluminium I bought produces cuts like your pictures, gummed up my bit and broke it.

Sharp, single flutes work well and keep the revs down.

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As Andy said not all aluminum cuts well, I was a machinist for a long time in the aircraft industry, and the 2 easiest and nicest types for machining I machined were 6061-T6 and 2024-T3. These are the types I think are referred to as aircraft aluminum. Keep at it you’ll get there and learn a lot of stuff you never knew you needed to know.

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Thanks for the replies folks.

I forgot to mention that I was running the spindle at about 14K IIRC.
I take on board what you say about materials. I got the sheet that I was using from a company that manufactures gangways for ships and tbh have no idea what grade it is.

I suspect with a 3 flute cutter I should have been cutting at perhaps 6K but not sure that slow a speed is good for my spindle/vfd.
I don’t currently have a smallish single flute bit so will look into getting one.
Not exactly sure which way I’d go for the tapered ball though. I think it was a 1/32 radius at the tip and I can’t say I’ve seen anything like it that is touted as for metals?

Using a non tapered at that diameter is just asking for it to snap I think.

Cheers again
D
:slight_smile:

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The fewer the flutes you have on your bit the better. They sell bits for aluminum called o-flutes. It has just one flute.

Aluminum is a soft metal and will stick to your bits and gum it up if your bits are run too fast. Likes other have said, make sure your aluminum is one of the machinable types. Take a shallower depth of cut wen using a bit with 1 flute, and keep the spindle rpm as low as possible (most spindles need to run around 10k rpm to keep torque up. Makitas need to run faster I think around 12k. Double check).

Just do small test cuts first before trying to do a production run. After each operation, stop the spindle and look at the end of your bit. If you see aluminum sticking to the edges of your bit, you need to change something. That buildup can get worse over time, plug up the cutter, and cause the engraving to look bad or snap the bit.

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Yes that material is pretty gummy. There are many types of aluminum used in aircraft. They are all machinable. Just got to have the right feeds and speeds. With these hobby machines it is going to be a trial and error. Without having the rigidity of most metal cutting machines, as well as having good work holding as well. If you don’t have a spindle it is really going to be a trial and error. Using a hand router and not being able to get the rpms down low enough to not heat up that gummy material. When going at low rpms you will lose torque, I would say use a 2 flute upcut, with a setting on the router about 12k or dial at 2.5 and feed of about 32 ipm. That will give you about .0015 chip load. I would want to get the chip load hirer with that gummy material but you will probably stall that router, so it is what it is. Start with about .030 depth of cut and go up from there depending on how it sounds and feels. That is just my opinion.

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