One piece at a time

[Gra2472]

Good evening guys. I wanted to share my latest project with you. As a novice cnc machinist I am still learning the ropes, and the best way to do that is to make stuff.

This project started when I decided to correct the height of a wooden tank car that I bought a few years ago as an auxiliary water car. It has spend a lot of time in the back of the shop waiting its turn. The original trucks have an odd center post bolster design that is much too tall. Because of this, the couplers were a good three inches above the height of the rest of my equipment. Essentially rendering the car useless.

Since I have a pair of Allen arch bar trucks on the shelf waiting for their next assignment, I decided to replace the original trucks with the Allen trucks. This means that I would need to make a new body bolster. So, into my office I went. It took me a full day on the computer but I designed a new bolster in Fusion 360 which I am just now learning how to use. I find it much easier to use than Bobcad/cam which I had been using for the past couple of years. Unfortunately, Bobcad does not support 4th axis machining without a big upfront cost (future department) so I made the switch to Fusion 360 last week. I find that It is rather intuitive once you learn where things are in the system. As I found out though, I still don’t have all of the CAM settings quite right yet for my little mill, but I am getting there.

I milled the bolsters out of 1x2x12 aluminum bar stock with a 3/16 flat end mill. I started out running a 3/8 end mill, but it made such a huge mess flinging large chips and coolant around the shop that I had to switch to a smaller end mill. Eventually I will put the mill in a shower stall or something, but thats another project.

The total cutting time was about 2 hours per bolster. While they aren’t perfect, I think they turned out ok for a first try with the new software.

The original trucks with the high center pin style bolster are probably going to find their way into the pedal car project if I get to it this year.

Cheers and good steaming.

G

[zimirken]

Neat! That's funny, 1x2 aluminum bar stock and a 3/16 end mill are both staples on my CNC at work for making parts for the lines. Learning what feeds and speeds work well for a given end mill on your machine is a big part of the learning curve. The other half is figuring out good tool paths, especially to minimize the number of setups you have to do. My most used end mill size is 3/16 diameter 3 flute with 1.25in long flutes. For aluminum I run it at 8000rpm and 0.033mm chip size per tooth. I generally run 2mm depth and 1mm width of cut on aluminum. The deeper cut uses more of the flutes so they don't wear out as fast, I think the rule of thumb is an upper limit of 80% of the tool diameter. I also use fusion 360 and it's great, although it can be finnicky sometimes.

What machine is that? You'll want to enclose it in plexiglass so you can run an air blast / mist spray at the very least. Getting cut chips out of the path of the cutter is very important for cutting aluminum.

[Gra2472]

Thanks for the info! It seems that I use the 3/16 more than anything. The mill is a Grizzly G0704 that I converted to cnc almost five years ago. But, life gets in the way of hobbies. I just converted it to belt drive, so I can run about 5000 rpm. I run .0017 per tooth at a max depth of .125, which works well. The big problem I have is the mill head getting hot at that rpm. I definitely need to build an enclosure so that I can turn the coolant up.

[Gary Armitstead]

Hey Garrett,
IF you worked in the machine trades and you used a 3/16 end mill to cut that bolster, you would probably be "fired" JUST before lunch . It's a joke son, it's a joke . Seriously, CNC milling and manual milling are both similar in how the cutters are chosen to do a job. First, the rule is to pick the largest cutter you can find to ROUGH the part out. Your feeds can be faster and your speeds will be slower. Choose a tool path that can remove as much stock as fast as is feasible depending on the machine and the setup. BTW, your setup is great especially using soft jaws. I've worked with Fusion 360 tool paths a little. My goto program is MasterCam. There should be a tool path in Fusion that "might" be named LEFTOVER (?). Use that kind of a tool path with a slightly smaller cutter than you roughed with. Then you semi rough the remaining stock. Don't use the 3/16 cutter until to get to your semi finish or finish tool path. You'll find this process will be less nerve wracking on you AND the machine, Just a suggestion from an old timer .

[Bill Shields]

Careful about bearings overheating...

[SteveR]

I milled the bolsters out of 1x2x12 aluminum bar stock with a 3/16 flat end mill. I started out running a 3/8 end mill, but it made such a huge mess flinging large chips and coolant around the shop that I had to switch to a smaller end mill.

Use a 3/8 or 1/2" roughing end mill. Small chips, great throughput. Cardboard to keep the chips in one place.

SteveR

[Gra2472]

What do you use for coolant if you’re using cardboard to corral the chips?

[SteveR]

Plastic? Whatever you normally use? Adapt and innovate.
The point is that roughers are good at removing big chunks of metal quickly.
Just a suggestion.
SteveR

[Gra2472]

Hey Garrett,
IF you worked in the machine trades and you used a 3/16 end mill to cut that bolster, you would probably be "fired" JUST before lunch .

HAHA!! Yeah, I figured that I would be the laughing stock for using a 3/16 cutter to make parts. I just use it right now because I don't have a good enclosure around the machine. I started out with a 1/2" end mill but I felt like needed a suit of armor to protect myself from the flying debris!! So, I went to a much smaller size just to keep the home runs to a minimum (is baseball season after all). I figure I'll step up to a big-league cutter when I get the machine in something to save me from the flying razor blades.

G

[ccvstmr]

Garrett...

Doesn't matter how you get from Point A to Point B...as long as you get there. Your machine may be limited in what it can do based on the size and depth of cut. Everything has trade-offs.

Chip control? Get some corrugated cardboard and set that up around the mill. Confine the mess. Takes less time to clean up...allows more time for making chips. And if you don't have one already...consider getting a small shop vac to sit there alongside the mill for cleaning after each set up.

Good luck and keep sharing your progress here! Carl B.

[Soot n' Cinders]

In my experience roughing mills are amazing, and if your machine runs fast enough or can handle a large enough cutter then carbide is worth it for steel. HSS is still better for brass and aluminum to me since it can be sharper and will last longer in soft metal anyway.
Just as an example, I have some carbide roughing mills and have taken 0.06" deep cuts in steel with a 1/2" end mill without the machine breaking a sweat though coolant is a must for that.

And corrugated cardboard and some tape make for great chip control, easy to set up and easy to cut to fit with a razor knife.