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Paul Alciatore
10-17-2007, 01:27 AM
I was looking through some back issues of Projects In Metal today and came across an article titled "The 'Helix' Gear Hobbing Machine" by Terry Sexton in the December 1998 issue. It talks about a machine made from a set of drawings which he purchased from a company called College Engineering Supply in Codsall, Wolverhampton, England. At that time they apparently sold both the drawings and a set of castings (CI) for it's construction. The author did not buy the castings due to the expense of shipping but he made his own. The article has pictures of the machine, but no drawings.

I am wondering if anyone has built this machine with or without the set of castings and if so, what they think of it. Any of your thoughts or comments would be welcome.

Dr. Rob
10-17-2007, 02:18 AM
Building The Helix Hobbing machine was featured in a three-part series of articles in MEW around 2000-2001, written by the usual suspects at that publication. IIRC, drawings were also published.

This topic has been up here before, many years ago.

Terry Sexton moved on and wrote an article in HSM about the same time, about building a horizontal mill conversion dubbed the Phoenix. (i think he lives there)

Name to the contrary, the Helix doesn't do helical gears.

College Engineering Supply is, i think, still alive.

.

John Stevenson
10-17-2007, 04:35 AM
As Dr Rob says there was a three part article in MEW by Harold Hall on building this machine.

It was a taster based on the College Engineering kit in that the drawings were not complete in MEW so you needed to buy the kit and castings.

It also fell over in that he built it and that was that. No article on use, setting up etc. Even college engineering can't helop with that one, they just sell the kit.

The best guy to talk to on this machine is Dr Giles Parkes who has written a lot of articles on hobbing etc.
He has had one of these for years and knows how to use one. He travels to most UK shows with it and demonstarts it.

His has now been modified with an aditional work slide and train and can now do helical gears. He had this working at the Ascot show doing 45 degree bevels in Delrin.

The main limitation of these machines is their size and lack of rigidity, some thing like a 40 tooth 20 DP gear will have to be done in a series of passes as they are not rigid enough to do it in one pass.

If you have the room I feel the same as Terry that a horizontal mill will convert better to do the same job and still have use as a mill on other jobs.

.

J Tiers
10-17-2007, 08:08 AM
Building
Name to the contrary, the Helix doesn't do helical gears.

.

Whether or not that machine does, the only articles by Terry Sexton that I recall did in fact cover helical gears.

But I am pretty sure he had his own better setup for the mill. He had a separate spindle set up to drive the gear, a set of change gears to run it, etc, etc, IIRC.

lazlo
10-17-2007, 09:37 AM
Whether or not that machine does, the only articles by Terry Sexton that I recall did in fact cover helical gears.

You're half right Jerry :) The Helix/Jacobs gear hobber (from College Engineering in the UK) doesn't do helical gears. Terry's first article was building the Helix/Jacobs gear hobber from bar stock in the December '98 PIM.

He then published another set of articles in HSM magazine in 2002 "Hobbing Gears in a Mill" with a horizontal mill and dividing head, which of course, could cut helical gears.

Spin Doctor
10-17-2007, 12:48 PM
On any gear hobber in order to cut helical gears there are a number of equations that need to be solved for the feed and indexing rations that depend on the constant used. Plus the index ratios depend on the fixed ratio of the machines cutter to work rotation ratio. The Barber-Coleman I used to use at woirk was a 30 to 1 machine so IIRC the index was Number of teeth x Constant devided by 30+1 or 30-1 depending if the gear was a right or left hand helix. The feed gears need to worked out to another formula that I can't recall off hand right now. One thing we found extremely useful for finding feed and index ratios was a book called 14,000 Gear Ratios. The gear set-ups have to accurate to within 1.0001/.9998 IIRC to produce accurate helical leads I had a Barber-Coleman hob manual but it got tossed I think. Plus the hobber needs to have a means to rotate the cutter sufficently in relation to the center line of the gear. For a spur gear the cutter is swivled by the lead angle of the hob. For a helical the cutter needs to be swivled the helical angle of the gear plus or minus the lead angle of the hob again depending on if it is a left or right hand helix. Plus helical gears do not have the same PD and OD as spur gears. PD is Number of teeth/COS of the Lead AnglexDiameteral Pitch. IE a 20 Degree 40 tooth 10 DP gear would have a PD of 40/.939692621x10 or 4.2567" with an OD of 4.42567"*

* A warnignif any one ever treads into helical gear cutting. Do not ever stop the work spindle with out stopping the cutter. The gear indexing ration is actually advancing or retarding in relation to the cutter so you can not lrde in the cut like a spur gear. Plus if you are doing any of this stuff. Keep a notebook with feed gear ratios and index ratios for all of your solutions. Believe me it saves a lot of grief.

lazlo
10-17-2007, 02:11 PM
Do not ever stop the work spindle with out stopping the cutter. The gear indexing ration is actually advancing or retarding in relation to the cutter so you can not lrde in the cut like a spur gear.

True -- Terry had a very nice universal dividing head on his horizontal.
EDIT: Neill, is it OK to post a scan of Terry's gear hobbing setup here?

Lane has the ultimate setup, IMHO -- a Van Norman with the complete universal dividing head set :)