transmission project... CAD to CNC

[Ace]

I thought some people might like to know the process of taking a design from CAD to cnc machining and since I'm in the middle of a project right now I thought I'd post it up:

Some may know, some may not but I made a set of aluminum axles a couple of years ago using worm gears which have a 20:1 ratio in the axles. I haven't done much with the crawler for over a year... Mainly because we went clod's and I didn't think it could compete with a 4ws clod. Now talk of an "old school" class with short wheel base and 2ws has me thinking the old girl has some new potential.

With 20:1 axles, no normal tranny will work... I decided I'd need the same ratio as a clodbuster with a 10 tooth pinion... (50/10 * 44/15 * 40/16)=36.666:1 divided by my axle gives 36.66/20 = 1.833 for the tranny. I also wanted to make the tranny fit my final chassis plans so I decided I best machine one (two).

I started by selecting some appropriate gears from www.SDP-SI.com
Great website for small cogs and such.

then I went to CAD and designed the tranny:

[Ace]

Now that you have the design, you need G-code for the milling machine.

heres a sample of the G-code for the aluminum plate on the tranny:


N10G00G90
N15T1M6
N20G00X1.817Y1.1875
N25Z0.1
N30G01Z-0.062F2.1
N35X1.629F3.1
N40G03X1.629Y0.8125I0.J-0.1875
N45G01X1.817
N50G03X1.817Y1.1875I0.J0.1875
N55G00Z0.1

and so on for many more lines.

Gcode is a study all in itself. I'll explain the very basics here:

N10 is G90 which sets the machine to Absolute mode (as apposed to relative) i.e move to 1.000 in x is 1.000 from machine origin, not 1.0000 from where you're at now.

T1 is tool one , G6 is tool change (my machine doesnt have a tool changer so it ignores this)

N20 moves rapidly (G00) to X1.817 Y1.1875
N25 moves down (z) to .1 above the part
N30 is a feed move (G01) to X1.817Y1.1875 (straight line)

and so on, I could go on but this probably is boring people...

You CAN write G-code by hand. Sometimes I do for very simple parts or to make a hole for instance. Usually people use a CAM program to make the G-code. CAM allows you to draw the part (Usually a 2-d drawing) and then you pick the lines forming the path you want to mill and the CAM program will write the g-code coresponding to the path.

Now with G-code made, you feed the G-code into a controller. In my case MACH 2.

Mach 2 is a really cool program that you can download for free www.artofcnc.com good for 1000 lines of code. 1000 lines of g-code is a lot and you can make some pretty complex parts with the shareware version.

Here's a screen shot:

[jason]

Awesome thread. Hey Ace not sure what your plan is, but please take pics of the entire process from design to finished product.

[Ace]

I didn't take pics of the actual machining of the tranny parts but heres a shot of the mostly finished transmission cover and housing:

[Ace]

one problem I had with the design is how to hold it for machining... As you can see the part doesn't lend itself to being held in a vice. For these two parts I used double sided tape to glue the parts to a block of aluminum and then held the block of aluminum in the vice:

Then your free to machine the entire profile of the part as well as the inside of the part in one setup. After machining, you pop the part off the block and peel off the tape. You must take it relatively easy because the tape isn't as strong as holding the part in a vice or mechanical clamps but it works very well.

Here's the block to give an idea:

[Emaxximuss78]

Is it me or is the transmission case flipp flopped from the computer inmage to the milled part? In the computer imaget the mounting brace is on the left.
But on the milled part it is on the right?

[Ace]

Here's a picture of my cnc milling machine. whole thing weighs about 50 lbs. It's a TAIG 1019CR (I think that's right #)

Taig doesn't sell a cnc turn key machine. The CR is "cnc ready" meaning ready to add stepper motors where hand cranks normally go. Then you need a controller to drive the steppers. The controller hooks to the computer's parallel port and Mach 2 drives the parallel port. It's all pretty intimdating to a newcomer to cnc but it's really pretty simple. If someone want's more info I'll give it.

Here's my specific setup:

Taig 1019cr mill (www.taigtools.com)
Sherline stepper motors on all 3 axis (www.sherline.com)
Denvercnc controll box (www.denvercnc.com)

I bought all above from a2zmetalsmiths here in Denver. Tim is a great guy and very knowledgable on the subject. www.a2zmetalsmiths.com

My taig also has a Sherline spindle and motor. The stock taig motor is quite wimpy and I really like the extra torque of the sherline.

Btw, I also have a sherline manual mill and lathe and like them very much. I could never get the backlash on the sherline below about .005" and for a manual mill that is fine. For a cnc mill though that much backlash is a killer. The Taig mills have a 1/2" diameter lead screws -vs- Sherlines 1/4" screws. I think this is why the Taig has much better backlash (mines about .002 max) I could probably half that with some work on the adjusters.

a pic of my mill after cutting the trannys:

[Ace]

emaxximus, good eye!

Yep, it's reversed or mirrored or something

I layed it out in 2d for the CAM and then realized I was "cutting" the wrong side. Since I'm planning a 2 tranny setup and front and rear trannys are just swapped it doesn't matter so left it as is.

That last sentence will become more clear when the rig is finished...

I still have to make the lathe parts and add the mounting holes to the flange on the tranny side. Best get my butt away from this computer and get on it.

More pics to follow...

[jason]

When might we see this new rig?

[Ace]

good question... Anyone seen my motivation?

I've started now, that's a good step.

[RD400]

That gear box is sweet!! If you are looking to sell those, let me know, I will buy one

[JohnRobHolmes]

Ive been long wanting to start my own tranny, but I have just a manual mill and little experience on it. I figure that just making a plate tranny would be the easiest. I really like the idea of holding the block with double sided tape! I have been having the hardest time holding my parts securely. It seems to be the biggest hurdle for machining!

Great thread! It is motivating me to get my *** in gear for my gearbox!

What pitch and width gears did you use?

[Ace]

RD400, unless your axles are 20:1 ratio this tranny would be useless (unless your headed to the bonnieville salt flats!


John,

The tape trick was shown to me by some toolmakers at work, very slick. Try to get tape with very little thickness, the thinner the better (the good stuff is really just a thin (.005" or so) layer of glue with a backing. Also most of the tape is pressure setting meaning you have to smash the part and the block in a vice or c-clamp to get the tape to really "set". Make sure you don't cut into the tape with the endmill (like I did on the above pic!) cause the glue boogers from the tape will stick on your endmill and then the swarf will clog the tool in a hurry. I try to stay about .001-.002" above the tape and then file the "flash" off the part when done like de-burring.

[JohnRobHolmes]

dually noted.

No hints on gear pitch and width? it seems all the metric stuff sdp has is 5mm width or 1cm width, which seems very thin to me.

[Ace]

ohh, sorry. They are 32pitch... face with is .188"

14 1/2* pressure angle. A 1C 1-N32022 sdp-si part number to be exact (bottom gear)

and

Part Number A 1N 2-N32022 for the plastic idler.


Not 100% sure if r/c 32 pitch pinions are 14 1/2* pressure angle or 20* PA but they seem to mesh fine. SDP-SI only had 14 1/2* PA's in the size I needed so that helped my decision considerably.

[BultacoJim]

Ace,
You need one of these tool changers on your Taig.
This is one somebody designed for a Sherline Mill.

http://f2.grp.yahoofs.com/v1/kKuAQwK...oolchanger.MPG

Nice Transmission design.
I should have you design a 3-Speed Transfer case for my 1:1

-Jim