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Benchtop Gear Hobbing Machine

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vtcnc

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#1
Well, starting the new year off right! I'm now the owner of set of Prestech castings of which when finished, will allow me to hob my own gears. There was an auction on eBay over Christmas and I figured what the heck...

There are 11 iron castings manufactured by Preserved Technology LTD., of Oldham, England along with many prints and articles that the previous owner, Earl H., was very kind to make copies of and pass along.

Pictures of the castings:

99842-ed197734446b05d23b8b6a2685400603.jpg
The machine base. A little rusty, but easily cleaned up. Not bad for sitting a box for thirty years!

99841-e5e06d685fd892c557795f655e112916.jpg
Slide ways and brackets. The gear blank spindle housing block is tucked away on the right side of the photo.

99840-a5d786a572782777741e9f6a3d7767a3.jpg
Hob spindle housing casting (top center) and supporting brackets and angle plates.

List of articles at my disposal for the build:

Gear Cutting in the Lathe, by J.A. Radford, Model Engineer, 6 September 1968
Gear Cutting in the Lathe, by J.A. Radford, Model Engineer, 20 September 1968
Hobbing Device, Postbag by Geo. H. Thomas, Model Engineer, 17 December 1971
Hobbing, Postbag by K.P. Wood, Model Engineer, 17 March 1972
Gear hobbing, Postbag by Geo. H. Thomas, Model Engineer, 16 June 1972
A Gear Hobbing Machine, by T.D. Jacobs, Model Engineer, 5 July 1974
Gear Cutting, Postbag by G.H. Thomas, Model Engineer, 6 September 1974
Gear Cutting Machine, Postbag by T.D. Jacobs, Model Engineer, 17 January 1975
Gear Cutting Machine, Postbag by T.D. Jacobs, Model Engineer, 20 June 1975
Gear Machine, Postbag by T.D. Jacobs, Model Engineer, 1 August 1975
Gears and Gear Cutting, by T.D. Jacobs, Model Engineer, 19 September 1975
A Gear-Cutting Machine, by T.D. Jacobs, Model Engineer, 16 January 1976
A Gear-Cutting Machine, part II by T.D. Jacobs, Model Engineer, 6 February 1976
A Gear-Cutting Machine, part III by T.D. Jacobs, Model Engineer, 20 February 1976
A Gear-Cutting Machine, part IV by T.D. Jacobs, Model Engineer, 5 March 1976
A Gear-Cutting Machine, part V by T.D. Jacobs, Model Engineer, 19 March 1976
Gear Cutting, Postbag by C.H. Baker, Model Engineer, 7 May 1976
Gear Hobbing, by T.D. Jacobs, Model Engineer, 16 July 1976
Fluting Taps and Reamers, by T.D. Jacobs, Model Engineer, 6 August 1976
Gear Cutting, Postbag by F. Butler, Model Engineer, 3 September 1976
Gear Cutting, Postbag by I.G.O. Brown, Model Engineer, 3 December 1976
Gear-cutting, Postbag by T.D. Jacobs, Model Engineer, 17 December 1976
An Attachment for backing-off Milling Cutters, by Dr. A.R. Bracey, Model Engineer, 17 December 1976
The 1980 Model Engineer Exhibition Class "N" - Tools and Workshop Appliances, by D.M. Chaddock, Model Engineer, 4 April 1980
Home Made Hobs, by T.D. Jacobs, publisher unknown, drawings contained within dated 1982
The "Helix" Gear Hobbing Machine, by Terry Sexton, publisher and date unknown

There are also a series of articles included from Model Engineer's Workshop by Harold Hall and Chris Robinson. I can't place the dates. These are obviously later articles where the CES kit was either built or modified. There is some sorting out of these articles to do before I add them to this list. I realize my "bibliography" above is not to any academic standard, I'll clean them up as I go.

There is also an E-size drawing of the orthographic views of the assembled machine, gear cutting chart and associated parts list, of which there are 90 unique parts and 128 in total. The drawing is produced by Prestech, or Preserved Technology Limited copyrighted in 1986.

I expect this will take me a better part of 12 months to complete. In the spirit of the namesake of the company, I will first recreate the drawings from the articles in CAD. The current copies will be difficult to work from being small reproductions on letter sized paper.

My understanding is that this can be mostly machined on a 6" lathe, with the exception of the base. I'll bring that into work where I have access to a knee mill. The rest I'll do in the home shop this spring and summer on the 10F.

I'm not anxious about this at all, but very excited and know that I am in for a real challenge. I've made small tools, designed fixtures and machined simple things in the past, but nothing of this nature. Really looking forward to all this has to offer. Any thoughts about this project?
 
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#2
This looks like a very interesting project. Pulling up a chair and making a fresh batch of popcorn...
 

Ridjobradi

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Looking forward to seeing more.

Sent from my SM-T330NU using Tapatalk
 

Reeltor

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#4
Very interesting, here is a photo of a "jacobs hobber" good luck with your project.
img0.jpg
 

tweinke

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#5
Oh boy please keep us up to date on this it is very interesting!
 

taxodium

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Oh boy please keep us up to date on this it is very interesting!
The Jacobs machine is not unknown in the UK. I have seen some examples both plain and modified to include the option of spiral/helical gears. However before you get too excited the company Preserved Technology Ltd was dissolved in 1991. As far as I know noone is still making the castings. The design was ingenious, but limited in rigidity and only small cuts can be made, preferably in non-ferrous materials. So whilst a fascinating project if you want a number of identical gears in steel you'd be much better off with a commercial machine and if you only want one offs it's not much slower to use Brown and Sharp cutters. Only really useful if you want multiple fine pitch gears of the same tooth count in alloy or brass or insist on making your own hobs on a relieving lathe. Sorry.
 

Uglydog

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#7
Huge interested!!
Please keep us posted.
Will you be making prints as you develop the project? (hint!)

Daryl
Mn
 

schor

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#8
I'm here watching too.
 

vtcnc

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#9
O.k., made it through a "quick" read of all of the documentation...here are my initial thoughts.

@Reeltor - Your photo is straight out of Harold Hall's article in Model Engineers Workshop. The castings in this Prestech set are very similar to what I see in those photos and when I study the article details.

@taxodium - Key phrase: "fascinating project". I would like to learn how to hob gears - plain and simple. The company I work for manufacturers our own gears and we run about a dozen or so old Barber Coleman machines for our products. Many of them still have the WWII Defense Corporation badges on them. Those bad-boys were built to last! That experience has inspired me to really just want to learn and share while rising to the challenge of this project.

@Uglydog - Uhhh...yeah! Actually, what I have discovered is that the T.D. Jacobs prints in the Model Engineer articles are more or less irrelevant to the castings. His creation was fabricated entirely from bar stock and, judging from some of the anecdotal stories and letters, his base was made from roadside scrap! The Model Engineer articles authored by Jacobs are best suited for understanding the design and gleaning valuable hints at best. The Harold Hall article series in the Model Engineer Workshop are based on the experience Mr. Hall had in seeing the "Helix" machine and subsequently working a set of College Engineering Supply castings. These Prestech castings appear to be very similar to the CES set.

So, slight change of plans. Instead of recreating the Jacobs drawings, I'll first do my best to create some drawings of the Prestech castings. From there, I'll continue with drawings based on the Hall articles and develop my own prints. What is clear is that the final outcome will be my unique variation of the Jacobs gear hobber because there is little by way of precise drawings, directions and design to guide my way on this.
 

eugene13

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#10
Fasinating project, Good Luck
 

vtcnc

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The Jacobs machine is not unknown in the UK. I have seen some examples both plain and modified to include the option of spiral/helical gears. However before you get too excited the company Preserved Technology Ltd was dissolved in 1991. As far as I know noone is still making the castings. The design was ingenious, but limited in rigidity and only small cuts can be made, preferably in non-ferrous materials. So whilst a fascinating project if you want a number of identical gears in steel you'd be much better off with a commercial machine and if you only want one offs it's not much slower to use Brown and Sharp cutters. Only really useful if you want multiple fine pitch gears of the same tooth count in alloy or brass or insist on making your own hobs on a relieving lathe. Sorry.
Hi @taxodium...took a break from drawing the castings in Draftsight and perused through some of the copies of articles provided by the previous owner of the castings. It looks like the Robinson article in Model Engineer's Workshop tackles the modifications to the Jacob's gear hobber in order to allow for the cutting of spiral and helical gears. While I haven't quite determined what is different between the Prestech castings and those used in the CES set (maybe there is no difference) part of me thinks it isn't worth doing the project without incorporating Mr. Robinson's modifications into the final outcome...:confused:
 

vtcnc

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@pdentrem: After studying the Martin models, I can see four main differences that stand apart from the Prestech set of castings. Without having the benefit of machining the Martin castings or having run that machine, I think it is safe to say that the following four differences would be considered improvements over the Prestech castings:

  1. The base casting has what appears to be a chip/cutting pan cast into the base. After thinking about this, I'll probably fab up a chip tray for the entire benchtop machine to sit in while in use.
  2. The hob spindle casting appears to be more robust on the Martin model set. Once I have the drawings finished, you will see what I mean about the Prestech. With that said, I don't see this being a show stopper for my project at all. Maybe a future wishlist item if things seem flimsy.
  3. The cardan shaft support bracket, appears to be more rigid given the large gusset in the casting. My support is essentially an "L" with no gusset cast into the part. A gusset could be added though, and was one of the first thoughts to cross my mind when inspecting this Prestech component without the benefit of seeing the Martin model photos.
  4. There appears to be angular setting adjustments in the compound base and in the compound slide for both helical, spiral and possibly bevel gear cutting. This is evidenced by the arc shaped slots in the photos.
These photos were helpful @pdentrem, thanks! It gave me some things to consider as I further study the Robinson modifications for helical, spiral and bevel gear cutting.
 
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pdentrem

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#14
There is a YouTube showing the Martin under power. The link is in the Martin site.
Pierre
 

vtcnc

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#15
I've been busy creating prints of the castings and subsequent machining prints. See this thread for a sideline discussion regarding casting drawing standards and some reference materials.

As I created the prints, I naturally found myself thinking ahead on the plan to machine these. One of the features of this project is a vertical, cross and longitudinal slides in order to position work pieces in relation to the hob and to auto feed the work piece via the cross slide feed. The slides are of dovetail construction. One of Harold Hall's comments in his three part article is that he standardized the dovetails - I found this to be untrue.

For starters, one of the dovetail pairs interfered with each other by 1/16", so I was scratching my head on that one...this according to the drawings in the article. On another dovetail detail, two dimensions were reversed, defying the laws of physics.

I sketched out all of them in Draftsight, compared the fits and discovered that what Mr. Hall was going for was a 1/8" gib fit between the internal and external dovetail constructions. Armed with a clue, I picked the one pair of dovetails that would work for all three slides.

Drawing attached...
 

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vtcnc

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#16
Next set of prints: Item 10 - Longitudinal Slide. Basically working from the bottom of the three axis assembly and up. There are two prints: a casting drawing and a machined drawing. Drawing naming conventions for this project:

X-GH-IXX

First 'X' in the file name is 'C' or 'M' - Casting or Machined,
GH is for the project "Gear Hobber" - doesn't really matter here on the thread but it matters in my project files,
'I' is "Item" as in the itemized parts list. This is helping me key each of my prints to the articles and the drawings from the past, this is helpful again in my personal files, not really relevant to the thread,
'XX' is the Item No. noted in the original Harold Hall articles and CES and Prestech prints - which appear to be copies of each other.

I've included a casting print for those that may want to work backwards and create their own castings...I know its a long shot but I don't see any preservation of the casting dimensions happening anytime soon so I figured I'm the guy to do it.

Machined prints are essentially copies from the articles (if they exist in the article) or my interpretation of the article content and my own design - or a combination of all three.
 

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Tinmuk

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#17
Bryan,
Interesting project, i've thought about getting the Martin castings. Although i dont why since i have a Mikron 132 gear hobber already. I guess i just want make my own. I do have a small foundry and would like to make my own castings
 

cjtoombs

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#18
I've got the Martin castings for thier hobber. Interested to see your build.
 
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