Electronic gear hobber synchroniser

[J BROWNHILL]

Hello,
For a while now I have been thinking about cutting gears on my vertical milling machine
I used to cut them indexing each tooth with a formed cutter but hobbing seems very attractive, a job came recently needing 64t 32dp for a speedometer but the price of the cutter plus my time becomes excessive.
I have been looking at old posts on the forum regarding the unit John Stevenson made from the article in MEW108 (I have a copy) I would like to make this, John said there were errors in the article.
Has anyone made this if so any help would be appreciated
Best regards
John

[djc]

I have been looking at old posts on the forum regarding the unit John Stevenson made from the article in MEW108 (I have a copy) I would like to make this, John said there were errors in the article.

I think it was the veroboard layout that had the error. I believe a corrected version was published in the next issue.

I think the key issue with it is that you have to put the correct number of pulses into in per revolution of the spindle. You cannot just plug any old encoder into it. I believe JS geared his encoder off the spindle with timing pulleys.

Are all the IC's still easily available? The core of it was a divide-by-n chip. Nowadays, this is more easily done with something like an Arduino, but for speed, you have to forego some of its built-in functions and write closer to the AVR C that underlies the Arduino environment.

[skunkworks]

You can make a totally flexible gear hobbler with linuxcnc...

http://wiki.linuxcnc.org/cgi-bin/wiki.pl?Hobbing

[J BROWNHILL]

Thanks djc,
Firstly all the ics and compatible switches are still available through ebay .
Secondly on the third reading of MEW 110 I found the corrections not a diagram but a small note on page 11
Thanks
John

[J BROWNHILL]

I have ordered the ics etc but I need some help with the encoder
I would like to use a ready made encoder 1024 p/r but which type would suit the circuit and what would the connections be, there seems a large variation to choose from

[djc]

I would like to use a ready made encoder 1024 p/r but which type would suit the circuit and what would the connections be, there seems a large variation to choose from

A standard two-channel encoder will work. It has A and B channels and power and ground. Perhaps you could give examples of the variations you have seen.

At the risk of repeating myself, you have to have an encoder that puts out 4000 pulses per rev. of the spindle. This is also assuming you have a 40:1 ratio on the (mechanical) gearbox at the workholding end of the setup.

JS used a 1024 ppr encoder but then had to gear it up (125:32) using timing pulleys to get the 4000 pulses. You can chose a different pulse count and different gearing if it suits you. My gut feeling is that high count encoders have greatly reduced in price and timing pulleys have greatly increased in price. Do the cost maths and see what is best for you.

Have you read everything you can find on this topic? JS posted somewhere that he had abandoned this set up and moved to the LinuxCNC setup posted above.

A further modern development is to look for something by Macona here (and on YT). Modern SERVO motors have in-built electronic gearing, so you just connect the encoder directly to the servo amplifier, set the ratio and away you go. No need for ICs or veroboards.

EDIT: as a starter, look on eBay for E6B2-CWZ6C incremental encoder. Very cheap, and in 2000 ppr, you can use much simpler 2:1 gearing.

[skunkworks]

Sir John talking about it

http://bbs.homeshopmachinist.net/thr...hlight=hobbing

[J BROWNHILL]

Hi,
I looked at the encoder suggested yes I think that would work so I will order one(cheap on ebay)
I can gear up the encoder easily from my hob spindle 3" dia with toothed belt.
And I also have a 40:1 dividing head
Thanks