Servo Driven 4th Axis for CNC Mill

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awemawson:
I can't mount the motor yet as those 5/16" UNF cap screws haven't arrived, so time to investigate the ROD450B/125 encoder and it's mount.

The TNC355 Heidenhain controller can only accept either 18,000 or 36,000 counts per rotary table revolution. Now my table worm has a ratio of 90:1 and the gear train has a ratio of 4:1 and the encoder gives 125 count per rev. Multiplying up we get 90 x 4 x 125 = 45,000. Divide 36,000 by this and we get 0.8, or a ratio of 20:25.

Somehow I need to gear the servo motor to the encoder, slowing the encoder by a factor of 20:25

Here are the bits we are dealing with

awemawson:
The current plan is to mount the encoder at the side of the servo motor on a specially milled housing allowing me to run a timing belt between them. The servo motor will have a 40 tooth pulley, and the encoder a 50 tooth one. Mounting the encoder facing the other way will shorten the whole assembley which is a 'good thing'

Masking tape mock up below :ddb:

Andrew

awemawson:
This morning's job was to make an adapter for the ROD450B encoder. It was to allow movement on slots to tension it's drive belt, and to bring the shaft position to the same axial point as the SEM servo motor.

Only two little 'funnies' during this process:

Firstly we had a power cut as I was downloading the G code file to Heidenhain controller from my PC, it wouldn't have been an issue, but I'd not saved the CAD drawing of the cut outs - no big deal as it's only a few minutes work to re-do it

Secondly, for some reason Featurecam refused to cut one of the adjusting slots, claiming that the tool was too big despite using the same tool for the other identical slot. I had to lie to it !

So here we are:

a/ the blank adapter cut from another bit of that (was) 20 foot plank of 100 x 20 aluminium - the notch is for clearance on the servo motor

b/ same thing holding the encoder

Andrew

awemawson:
Today the Postman brought me the oil seal for the Servo Motor shaft, and the 5/16" UNF cap screws, so I've been able to mount the motor and try the gear mesh, which seems ok. No doubt it'll sound better when filled with oil - it's just lightly oiled at the moment as I'm not convinced the original housing flanges are oil tight and while it's on the bench I don't want it dribbling everywhere !

The servo motor is 140 volts 26 amps peak, so I was surprised how it runs quite well on 24 volts at less than an amp for testing.

Now I'm working on the CAD for the housing that holds the encoder onto the back of the servo motor, fighting tangent snap modes in Featurecam :scratch:

Andrew

Pete.:
How does the machine Interface with the 4th axis drive electronics Andrew? Do they simply both comply to a standard?

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