Machining a coupling rod

//Machining a coupling rod

Machining a coupling rod

So as my next project on the CNC Mill i wanted to machine a coupling rod, I was interested to see if all machining could be CNC using as many OPS as needed. So heres the design.

With thanks to all the folks that have helped with suggestion with this project
Andy Berry, Bengineer, etc.

So basically i would like to side mill the profile, then rotate the fixure and side mill along each side of the rod. The flutes to be done with a bottom and side cutter or a ball end??

The holes on the left are 9/16″ and the one on the right is 17/32″, the length between centers is 7.125″, the thickness at the tallest height is 3/8″ and the lower height is 1/4″.  The stock will be 3/8″ x 1″ x 8″ EN1 mild steel.

So i though i would try and do all machining on a custom fixture.

1) Install Ali blank into vice on parallels

2) Face off and profile to a known size 1/4″ down all the way around.  This will give me a number of datums to use.

3) With the datum set for Back Left, spot drill and then peck various sizes upto a few thou under size and then ream to 17/32″


Machinig the Coupling Rod.

OP1 – Face and mill the shelf on the the right side, repeat for top and bottom

Then flip the part and repeat


Profile the couple rod – roughing pass Alpha Mill – 10mm 2 flute insert tooling (pic shows a 3 flute for example)

Feeds and speeds – The supplier has given me the following information only:

“I would start at

2227 rpm

267 mm/min feed (if using no more than 50% of your cutter dia)

Doc- this will just depend on your machine rigidity- if you feel your machine can take 1mm DOC then do that….this is something I cannot suggest as I am not running the machine.”

If you are only using up to 20% of your cutter dia on a side cut the feed rate would be 500mm/rev


So we know
Vc (surface speed) recommended for this tool on medium steels: 50 – 80 m/min
Fz (feed per tooth) recommended for this tool on medium steels: 0.05 – 0.08 mm/tooth

We can calculate the RPM:
RPM = Vc / PI / DIA * 1000, so
RPM = LOW 50 / 3.14 / 10 *1000 = 1,592 and
RPM – HIGH 80 / 3.14 / 10 * 1000 = 2,547

We can calculate FEED:
FEED = n x fz x Z (where n = RPM, fz = feed/tooth, Z = number of flutes)
FEED = low 1592 x 0.05 x 2 = 159 mm/min
FEED = high 2547 x 0.05 x 2 = 254 mm/min


Toolpath – 2D Adaptive Clearing.  An alternative would be to machine each side seperately, this would allow clamping of the center section.

Finishing op is 2D profile, single pass full depth of tool.  6mm 4 flute Carbide.

By | 2020-04-17T02:02:20+00:00 April 16th, 2020|Uncategorised|0 Comments

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