Thread: NEED HELP - Brass Milling

Hi Mike
If you have a look at the projects thread you will see that I milled some brass on Sunday. I mm dept of cut with no burr on top edge.
Brass like aluminum can vary considerably in hardness depending on the composition of materials. I use scrap yard brass so I have no idea on the quality or hardness but seem to make a job of it eventually.
I find the best trick is shallow depth of cut. A very light first and second pass produces smaller edge burrs that can usually be removed with your thumbnail. If you are using Aspire this will mean having two toolpaths for the same job as you cannot vary the depth of cut. Just do a couple or three or four runs at say 0.05mm pass depth then change your toolpath file with one that is a bit heavier. Depending on the size of the cutter you might only increase it to 0.1mm pass depth next time.

Yes your spindle speed is a bit high and feed speed also too high for the way I operate. I was running the mill for my job so 3,000RPM and 400mm/min.

Other methods are to do a roughing cut with an internal offset of say 0.05 then and when that is finished you do a full depth cut up to the line. This gets rid of any step lines in the sides of the job too.

Another thing you can try is to cut the job again and sometimes the slight (micron or less) movement in your machine or spindle run out is enough to improve the burr. Do it again if it starts to work. This is why I advocate never to demount your job until you are satisfied it is the best cut you can produce.

Yes you can use wet and dry to remove the burr. Used 600 then 1200 wet and dry to remove scratches and burrs on jobs before. I do have a home made buff with 6 inch stitched and loose cloth wheels and a few grades of tripoli (??) soap. It works a treat but make sure you use a flat sanding block and don't stay too long on the buff or you get slightly rounded engraving on the top edge.

If the mill bits are second hand don't gauge the sharpness by feeling the flutes above 1mm from the end of the cutter. All cuts are done with the tip so sharpness is at the tip of the cutter and not higher up the flutes.

Sorry for the length of the post but you did ask.

Rod,

Thanks for the great and very detailed reply.

I have a couple of questions/comments;

1. I used a 0.5mm cut for this job but your logic on using shallow cuts at 1st is intuitive and a good idea. As you mentioned I also bought my stock from a scrap metal yard and I have no idea of the grade. I will also give the end mill a grind on my grinder to ensure a good edge

2. With respect to using emery to remove any imperfections, my understanding of your comment is that a light sanding and bugging of the piece with an appropriate compound should allow me to remove the emery marks and the burrs - also with the understanding it needs to be slightly conservative close to the edges of the cut to ensure the edge crispness?

3. I did see your compass project and was very dissapointed in my efforts having seen your output. Once again you produced a very nice quality product which looks great and seems to meet its functional requirement. It's good that you and Greg keep posting items so we can aspire to produce good products too as well we can learn from your errors.

First off I'll say I don't know anything but... Did you use lubricant and are you climb or conventional cutting your last pass?

I know Aluminum cuts much better when you use kero or similar (diesel) as a lubricant and that Climb cutting is better for finish passes. As its a soft metal I would assume brass is similar and suffers from the friction of the tool on the part and rewelds chips so to speak.

Just my $0.02 worth.


Cheers

Cheers Mark for the reply.

I ran the job again last night with a 3 flute end mill using kero. This worked a treat and seems to have cleaned a lot of the burring from the edges. The unit was run in conventional and then climb milled for the last run so this should have been okay in the 1st run. Looking at the difference in the two runs i believe most of my problem is due to the cutter and the 1st cutter may not be suited to brass. This is always an issue with cutters that you have no data on, you not quite sure that they are suitable for the task. Must try to find the data sheets from the spec number on the unit.

I have to mill some more today to finish the project off and i'm going to try the light cuts to establish the edges and then clearance cut the guts of it.

For future refence if anyone is interested.

I resolved my issue by running the job twice.
Pass 1 provided the milled profile down to the desired depth.
Pass 2 cleaned up the outer edges and gave me a level depth.

I used the same program for both passes, but I ran Pass 1 at 150 mm/sec and Pass 2 at 450mm/sec. I used Kero as Lube/coolant on both passes.

/M

Hey SFmike hows about a finished photo, would like to see what you're knocking up there mate ?

Sure, I have to blacken it and clear coat over the top. Once i get this done i'll post a finished pic.

As promised

Fantastic effort there SFMike looks great , thanks for sahring

Hi Mike,
Very professional.
Can I impose and ask you to post that in the projects log. Trying to get a good collection of jobs in there so people will get motivated to make more machines.

Mike,

It does look great ... what size is the finished piece?

Cheers,
Alan

The unit is about 500 (W) and 300 (H). I mounted it last night to one of the pillars on my front gate and in hindsight it would have been better at 80% of that size. One of those things where you make it, mount it and wish it was a little different.

I learnt a lot on this project, so I am pleased it came out okay. I know where to do things a little differently next time.