Author Topic: Rear Cutoff Toolpost for the Cowells  (Read 2244 times)

Offline Bobsmodels

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Rear Cutoff Toolpost for the Cowells
« on: May 30, 2018, 01:31:16 AM »
As you can see from the photos I made a rear cutoff toolpost  for my Cowells.  This is the first of three attachments I am making, the others are a boring bar holder and 4 position toolpost.  I think I can get started using the lathe efficiently with those three.  I am sure there will be others, maybe a quick change toolpost.  On a small lathe I worry about repeatability of a quick change.  A microscope adaptor at first glance looks a bit tricky to make.  I am not sure about the torque on the crosslide, although the Cowells crosslide looks sturdy.  I could mount it on the platform, but then you need a method of movement so the cut does not move out of the field of view.  I have seen a setup using a linear bearing platform. 

For the rear cutoff toolpost  I used an extra Sherline rear toolpost that I had and made a spacer block to get it up to the center height of my Cowells. I debated whether to just make one from scratch or make the spacer.  Given the Sherline was available and was machined for the blade setback I decided to re-use it.  I measured the center height of the Cowells over the crosslide table at .988.  My Sherline Toolpost height is .943.  I made a .045 spacer on my surface grinder and holder lines up and fits nice on the lathe as you can see from the photo.

Once I get a set of collets I will make the boring bar holder.  The 4 position toolpost is underway.

More later

Bob

Offline craynerd

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Re: Rear Cutoff Toolpost for the Cowells
« Reply #1 on: June 19, 2018, 03:19:39 PM »
Hi Bob, What is the size of the cutting tool / parting tool that it takes.

I made one from scratch a good few years back and sold it with the lathe. Iíve just got hold of another Cowells and it is one of the few attachments I am missing.

Nice build. Cheers, Chris

Offline b.lindsey

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Re: Rear Cutoff Toolpost for the Cowells
« Reply #2 on: June 19, 2018, 04:19:21 PM »
That looks good Bob. You are getting your little "C" fitted out nicely  :ThumbsUp:

Bill

Offline Bobsmodels

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Re: Rear Cutoff Toolpost for the Cowells
« Reply #3 on: June 20, 2018, 07:14:57 PM »
Chris

Sorry I missed your question.

The cutter that is in it - Acme Grooving Tool  P-1-N  M-3  10/06   It is T shaped.  The top of two different ones were .99 and .96  MM, and they were both about 12MM high and about 90mm long. These came from Sherline and I doubt I will ever need a replacement.

Bob

Offline Chipswitheverything

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Re: Rear Cutoff Toolpost for the Cowells
« Reply #4 on: June 24, 2018, 07:56:09 AM »
Bob, you have mentioned making a boring tool holder for your Cowell lathe.
 This gadget that I made a while back for my Cowell might just interest you, it is a Swing Clear type of boring bar holder, along the lines of the one that Martin Cleeve wrote up in the Model Engineer mag for the Myford lathe, back in the '60s.
  It works particularly well on the little Cowell, because it saves winding the carriage back a long way on the leadscrew for gauging purposes, or moving the cross slide for measuring and losing the reading.  Once the tool tip is clear of the bore, you just flip the thing out of the way of course.
 Just made out of BMS sections, the fit of the arm between the side plates wants to be a nice snug light push when it is down.   The tool is from 1/4" silver steel, various sizes can be made up to suit, and the tool holder incorporates its own convenient height adjustment!, very handy.     Dave
 

 

Offline b.lindsey

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Re: Rear Cutoff Toolpost for the Cowells
« Reply #5 on: June 24, 2018, 02:01:35 PM »
Interesting idea Dave, I can see where the height of the tool can be adjusted, but once it is swung down into cutting position, what holds it there? Just the downward force of the cut?

Bill

Offline Chipswitheverything

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Re: Rear Cutoff Toolpost for the Cowells
« Reply #6 on: June 26, 2018, 04:50:58 PM »
Hi Bill, thanks for your interest.   It's true that the cutting force will tend to hold the tool down, but what really secures it is the light push fit of the arm between the side plates that I mentioned above, it snucks down to give excellent rigidity.  When I flip the arm up, I usually do the first portion of the upwards movement by just using a pencil like scrap of wood as a lever between arm and base to save giving a yank upwards, though it will come up with a tug for all that.

 It's easy to get that snug fit when making the tool, because the base and side of the arm can be skimmed and/or draw filed together in situ.  Note that there is a shallow relief section in the centre area of the arm so the fit is at hinge and near the tool holder part.   I must say that it is a tooling gadget that works very well on the Cowell.
 
 I have made a "full size" one for my Myford, but because it's easy to run the carriage back on the big lathe it gives less advantage than on the Cowell - as anyone who gets fed up with frequently winding the Cowell carriage back and forth a long way when using the usual toolpost mounted boring tool will soon find out!        Dave

Offline b.lindsey

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Re: Rear Cutoff Toolpost for the Cowells
« Reply #7 on: June 26, 2018, 05:03:57 PM »
Thanks Dave, I should have read the last part of your post more closely, but thanks for clarifying.

Bill

Offline Bobsmodels

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Re: Rear Cutoff Toolpost for the Cowells
« Reply #8 on: June 26, 2018, 07:47:45 PM »
Dave

Just saw this today.  I had posted my boring bar holder a couple of weeks ago.

 http://www.modelenginemaker.com/index.php/topic,8202.0.html

 I like the flip up idea.  Same cranking issue on a sherline also.  I usually moved the cross slide in and out for checking, but as you mentioned you need to not loose the mark where you were and this does solve that problem. 

Very nice attachment.

Bob


Offline Chipswitheverything

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Re: Rear Cutoff Toolpost for the Cowells
« Reply #9 on: June 27, 2018, 07:51:15 AM »
Thanks for your comment Bob.   One thing that I might mention is that I haven't put any tongue to fit the cross slide slot(s) on the bottom of this swing clear tool, as I wanted to be able to make small adjustments to the angle of the tool re the bore rather than be locked in the straight ahead position.

 I haven't had any problem with the device wanting to shift at all, despite the single Socket screw / tee nut fastening - but the base area is quite large, and one could always interpose a thin piece of paper between base and 'slide for extra friction.  ( Or fit a tongue...)    Dave