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magnet-man
12-01-2005, 11:35 PM
Does anyone know anything about his gear hobbing machine? The project was by Terry Sexton in the December 1998 Projects in Metal. I saw a reference to it in the May 2002 HSM and was wondering if it is worth purchasing the project book for that year. I need to make very small helical gears and thought this might be a good place to start.

Dr. Rob
12-02-2005, 01:26 AM
There used to be a kit sold commercially by College something in the UK, made from castings. It was called either the Helix or something else; I don't remember.

In any case, IIRC, it does NOT cut helical gears.

Doc.

PS: ...although his articles are otherwise greatly enlightening. Suggest reading more, and doing searches on this board as well as PM board.



[This message has been edited by Dr. Rob (edited 12-02-2005).]

Holycross
12-02-2005, 01:48 AM
Doc,

Was this whe casting set you had seen?

http://www.collegeengineering.co.uk/Castings/582.htm

Mark

Dr. Rob
12-02-2005, 02:38 AM
Yeah, College Engineering- that's it.

MEW magazine has done several write-ups about it.

John Stevenson
12-02-2005, 02:47 AM
Correct,
This machine will not cut helicals, ' as is'.
Giles parkes has one and he was in the process of modifying it to do so when he got side tracked by buying a full sized machine that will.

Last time I spoke to him he had modified the slide mounting so the helix angle of the hob could be increased from the limited amount of travel it has.

The next drawback is that you need an extra set of drive gears to time the traverse to the hob rotation to get the helical angle you need. Fast train equals a short helix and a slow train equals more helix angle.

I have got by this by using an electronic hobber with encoder ans stepper motor drive that does away with this extra gear train.

Have a read of this post:-
http://bbs.homeshopmachinist.net//Forum1/HTML/004609.html

John S.

sch
12-02-2005, 10:55 AM
There was a reference to further development of the gear hobber project in the 2003 HSMBB article: was the article in MEW 108 by Brian Thompson the culmination of that effort?
Steve

John Stevenson
12-02-2005, 11:08 AM
Steve,
Brian Thompson was the inovator of this idea. He worked the problems out and built a working unit to attach to his lathe.
This was shown at a UK Model Engineering show where I saw it, contacted Brian and bought a prototype 'black box' off him and adapted it to fit a big horizontal mill.

I then found an electronics guy in the States, Don Foreman who designed a better board and circuit.
I bought some off him and sent them to Brian to be built with all the parts to do two boards.
I had one Brian kept the other for doing mine.

All along it was Brian's idea to write an article. Dave Fenner the editor of MEW asked me as mine was further along than Brian's and was doing helicals etc but it was Brian's baby and only right he got recognition for it.
I suggested to Brian that he transpose the purpose made board for veroboard so that it could be made better in the home shop which he did.
BTW there is an error on the board in MEW 108, this had been corrected by printing a new board layout in ME109.

Brian is happy for me to take this where I need to go, all he wanted was recognition for his early work on this.

Sir John.

[This message has been edited by John Stevenson (edited 12-02-2005).]

magnet-man
12-02-2005, 11:42 AM
John,

So if I wanted to do this black box and stepper motors, where do I go to get the information to build one and the software to compute the steps. I have lots of stepper motors and drivers.

Thanks
Bill

[This message has been edited by magnet-man (edited 12-02-2005).]

John Stevenson
12-02-2005, 11:51 AM
Bill,
There is no software.
There are three thumbwheel switches that select the number of teeth to be cut and a switch to revers the drive for RH and LH hobs.

All that is needed is an encoder mounted on the hob arbor, the circuit board that works the divide calculations out [ published in MEW V 108 and ammended in V 019 ] a driver and stepper motor driving a 20:1 worm geared head.

There is a lot of detail in the post I have linked to above.

John S.

magnet-man
12-02-2005, 03:01 PM
Everyone thank you for your replys. One last question for now regarding gear hobbing. Where do I find these less expensive asian gear hobbs that Terry mentioned in his article. I have looked but can not find any to suite my needs.

Are most people making their own hobbs?

snowman
12-02-2005, 04:58 PM
Are those castings actually available anymore...or have they quit?

If so, does anybody know the approximate price?

-Jacob

Holycross
12-02-2005, 11:03 PM
John S. ,

Do I need both articles for MEW 108 and 109 to build the controller?

Jacob ,

The website I posted above list the price at 128 pounds about 230 dollars. Castings weight of 20Kg, about 44lbs which is right at the limit for air mail postage. Probably 60-80 bucks in postage to get it sent here in the USA.

Mark

John Stevenson
12-03-2005, 04:44 AM
You need V 108 for the article and the ammended board from V 109 [ there were two breaks on the veroboard missing ]

I have spoken to Brian on this and he has no problem now it's been published with people copying it, makes sense http://bbs.homeshopmachinist.net//biggrin.gif

As he also has the rights to this article he's given me permission to scan these two articles and post them.
This I will do later this weekend and post the links here.

Sir John.

Holycross
12-04-2005, 12:47 AM
Sir John,

Please thank Brian for being willing to sharing this information. Thank you as well for posting the information.

Mark

snowman
12-04-2005, 06:33 PM
John,

Definately interest in the scan. Just dont want you to think that because not too many people responded there isn't interest.

-Jacob

magnet-man
12-04-2005, 07:07 PM
John, I am waiting with baited breath for the scan.

John Stevenson
12-04-2005, 07:51 PM
Sorry only just found the corrections, they were in V110 not 109.
Late here now, 1:45 am, now I've got al the relevant pages sorted I'll scan this tomorrow.

John S.

John Stevenson
12-05-2005, 12:23 PM
Five pages, seperate scans in case you are on dial up, roughly 300K per scan, if I go lower I loose resolution.

The mods are marked on page 5 with an annotation and I have put two crosses on the extra cuts.

http://homepage.ntlworld.com/stevenson.engineers/lsteve/files/page1.jpg
http://homepage.ntlworld.com/stevenson.engineers/lsteve/files/page2.jpg
http://homepage.ntlworld.com/stevenson.engineers/lsteve/files/page3.jpg
http://homepage.ntlworld.com/stevenson.engineers/lsteve/files/page4.jpg
http://homepage.ntlworld.com/stevenson.engineers/lsteve/files/page5.jpg

Sir John.

LES A W HARRIS
12-05-2005, 05:53 PM
John,

Many thanks.

Les H.

Joe H
12-06-2005, 05:24 AM
John,
I was considering how to hob helical gears on my shop-made hobbing set up on a horz mill. It is similar to the Helix (CES) with the change gears and driveshaft. In a post from a while back (rather long -below) it appears the velocity problem with a driveshaft employing universals will affect a machines ability to hob helical gears. I had figured that I would have to add a set of bevel gears so that the input and output shafts of the universal drive shaft could be made parallel. It would be interesting to see if Giles runs into this problem if he continues with the Helix modifications. This, of course, would not be an issue with your electronic hobber or with a gear hobing machine as they do not employ the universal drive shaft. One of my current (and uncompleted) projects is an adaptation of Giles Parke's Relieving Attachment from MEW 57.


http://bbs.homeshopmachinist.net//Forum1/HTML/000782.html

Joe

John Stevenson
12-06-2005, 07:04 AM
Joe,
Provided that the drive shaft have equal universal joints and they are timed they will cancel out.

From the "Principle of Universal Joints"

Although constructional details can differ widely between one maker's product and the next, UJs fall into two groups, identified as constant velocity and non-constant velocity joints. Huco's examples work on the Hookes or Cardan principle and are of the non-constant velocity type.

What this means is that for a given operating angle, the output velocity fluctuates, even though the input velocity is constant. These fluctuations result in the output gaining, then lagging, with respect to the input, twice in each revolution to an extent governed by the operating angle. The fluctuation is predictable and is a function of angular velocity and operating angle.

At low speed, or on manual operation, the fluctuations will be of interest only in calibrated applications. At higher speeds, they will increasingly give rise to torsional vibration. Constant velocity output can be restored by using a double joint or by connecting two single joints back-to- back.
******************************

Sir John.

magnet-man
12-06-2005, 07:24 AM
John can you update the links in the previous mention thread. I would like to see that prototype.

John Stevenson
12-06-2005, 09:50 AM
I'll try but I lost a load of stuff in a HD crash.
I'll look tonight our time.

[Edit]

Found them, they just needed renaming after an ISP update.

http://homepage.ntlworld.com/stevenson.engineers/lsteve/files/CES%201.jpg
http://homepage.ntlworld.com/stevenson.engineers/lsteve/files/CES%202.jpg
http://homepage.ntlworld.com/stevenson.engineers/lsteve/files/CES%203.jpg
http://homepage.ntlworld.com/stevenson.engineers/lsteve/files/CES%204.jpg
http://homepage.ntlworld.com/stevenson.engineers/lsteve/files/CES%205.jpg

Old post has also been modified.

Sir John



[This message has been edited by John Stevenson (edited 12-06-2005).]