Duncans Metal Pages
Jacobs Hobber
Last updated: 30 Nov 2016


1: Work head
2: Vertical slide
3: Base
4: Long' slide
A: Electrics
C: Links

An interesting article I've stumbled across recently is "A Gear Cutting Machine" by T.D. Jacobs in Model Engineer, January through August 1976.  This looks like an interesting long term back burner project, utilising structural steel mainly and some bar stock.  I plan to use castings instead of structural steel, so if it doesn't work out, I can simply melt it into something else ;-)

Jacobs describes the construction of the machine in seven sections, so I will try and work through it in that order.  An extra couple of sections have been added, namely electrical and links/resources.

The original article is sketchy about some details (for example how to hold the gears onto the shafts), an attempt will be made to fill the gap through these pages.  There are some deviations from the original game plan, for example I'm using metric sizes for the fasteners instead of the BSF/BA threads simply because I have large numbers of the former.  Shaft sizes are being kept at imperial sizes to suit the lathe change gears already to hand.  Where one of the sections below shows no image available, it means that no work has been started on that section yet.

1. Work head.  Details the work holding part of the machine to which the gear blank is attached.
2. Vertical slide.  Simple slide to which the work head is attached.  With sections 1 and 2 done, I believe some primitive gear cutting can be done in the lathe.
3. Base.  The original article details a base made from constructional steel items, U channel and angle.  I would really like a cast aluminium tray for this to collect any coolant that drops off the cutting head.  Planning on this has come full circle and it's back to constructional steel due to lack of time.
4. Longitudinal slide.  Another simple slide to which the cross slide will be attached.
5. Cross slide.  Sits on top of the longitudinal slide and holds the vertical slide.  Power feed is used on this item.
6. Cutter head.  Driven by the motor/countershaft, this holds the cutting tools (hobs).
7. Index worm drive.  A neat drive mechanism complete with universal joints to rotate the gear blank as it is being cut.
A. Electrics.  Jacobs favoured an overhead drive from pulleys in his workshop - I don't have any of these, so it's an AC motor job.
B. Links/resources.  List of links to other pages and resources for the Jacobs gear cutting machine and variants.

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Warning: These pages consist of images and descriptions of equipment which can reach high temperatures creating hazardous and potentially dangerous situations.  These pages should not be taken as a step by step guide on how to construct any items or carry out any particular procedure, nor should any references to safety contained herein be taken to guarantee safety in all situations.