View Full Version : Potter & Johnston shaper question

09-01-2014, 09:07 PM
Being curious can be a real liability sometimes!! :)

I had a job show up recently, that after careful consideration, I came to the conclusion that the only way to accomplish the task was on a shaper. That may be a separate story worthy of another thread, but bear with me for a moment and consider this question.

I have a shaper that was handed down to me from my father who received it probably 30 years ago, from a mutual friend, who became jealous of the room that it took up in his shop after using it maybe once in 20 years, so he decided to give it to Dad and let it take up room in his shop. In those intervening 30 years, I can remember using it exactly once reworking the keyway in a large hub. My father on the other hand, used it rather extensively mostly as he didn't have a milling machine.

As part of the current job, I decided to do a little clean up and restoration to make the tool post/clapper feed slide operate a little less stiffly than the 50 or 60 years accumulation of dirt and crud dictated. As dis-assembly progressed, I became intrigued by a feature that I had seen on the unit before but had never taken the time to think about why it was there.

This Potter & Johnston shaper has a handy feature that allows for power feeding of the toolpost/clapper slide. The feed motion is supplied in part by a shaft that runs through the post that mounts said slide on the end of the ram. This shaft has a bevel gear on each end and in the middle of this shaft is a short section of worm thread. I think that this section of worm thread is supposed to drive a worm wheel that would be attached to the arm/lever that is circled in the photo below, however this wheel is missing on this particular machine.

But for the life of me, I can't see what purpose or utility this lever has in the operation of the machine. Given the complexity and expense of the mechanism it would seem that there would be some obvious intent or need for it's use, but it is obviously obvious only to others!

So I ask the question here, can someone tell me the purpose for this feature?

I initially thought that it interacted with the power feed mechanism as some type of stop as it is located near the adjustable pawl and ratchet assembly that advances the feed with each stroke of the ram. However I can't see how it would interact with the feed unless there are more parts of the mechanism that are missing. In the accompanying photo below that I found on the web, there seems to be a lever or mechanism that would rotate the toolslide about it's mounting post to allow the cutting of large radii, but this feature/mechanism is also missing from my machine.

What say ye great mavens of machine tool knowledge?? :confused:


http://i1042.photobucket.com/albums/b422/becksmachine/Potter%20%20Johnston%20shaper/cutindicator.jpg (http://s1042.photobucket.com/user/becksmachine/media/Potter%20%20Johnston%20shaper/cutindicator.jpg.html)

09-01-2014, 10:22 PM
Furthest thing from a machining "maven", like things mechanical and guessing however :confused:

Could it allow for a "rapid" traverse on the return stroke?

I mean larger shapers can have quite a stroke in terms of length but don't they move relatively "slow", I would assume you adjust even slower if the cut has good depth...yet they don't do much on return, except return...

And, as usual, is that another larger shaper in the background?

Edit: if you have not found other info yet, there is this http://vintagemachinery.org/mfgindex/imagedetail.aspx?id=5018, its an ad from the Canadian supplier at the time, talking about how it can shape internal curves

and this, http://www.practicalmachinist.com/vb/antique-machinery-history/potter-johnston-shaper-205033/ over on PM talking about power down feed, and missing bits plus how it works

there are some patent drawings on Google but I think they are a bit older, still one or two seem to show the mechanism(s) of the feed and there is an explanation if you scroll down far enough

Old Hat
09-02-2014, 12:06 AM
http://www.practicalmachinist.com/vb/attachments/f19/23225d1274890122-potter-johnston-shaper-img_2598.jpgCutting dovetails come to Mind?

You may also be able to shape an arc with that Lil' Angel.
I can't see it close enough.
Gemco offered such a head as well.

I have the indexing attachment for this Gemco.
But the arc-cutting part is empty on this one too.

Large die segments were shaped as a common opporation.
Picture rounding a corner 8" deep.
Some shapers were tilted, called punch shapers.
This way you could have a constant relief angle cut from the land (die-life to some)
all the way out the bottom.

this looks missing? no?

Optics Curmudgeon
09-02-2014, 01:24 AM
It's the automatic stop for the downfeed mechanism, if all the parts are there.

09-08-2014, 03:22 AM
A belated thanks to all who replied and especially to RussZHC for that patent info. And to Optics Curmudgeon for being absolutely correct in answering my question even though I initially didn't understand how it was possible.

Wow, anybody who thinks Old Hat talks in Most High Gobbledyspeak should try reading those patent narratives. :o

But it still didn't make sense until I got a little further into the auto feed mechanism. I couldn't understand how a positive/blocking stop would survive without breaking itself the first time it was used. However after further dis-assembly, I realized that it is a positive stop, but the feed motion is not. The ratchet and pawl mechanism also incorporates an adjustable slip clutch to vary the feed force.

This is an example of the delicate dance that is also present on most vertical turret lathes/boring mills. The problem is how to keep the backlash in the feed system from providing an erratic feed rate, caused by the force provided by the weight of the ram and associated tooling, being either greater or less than the feed force required.

In this case, because I was working in the interior of a hole with the cutting tool below the poke bar, the feed mechanism is trying to feed the tool down. So the lock for the tool slide must be tightened enough to prevent the combined weight of the tool slide, clapper block and poke bar from falling down to the limits of the backlash on every return stroke. Or maybe more importantly, to prevent the tool from trying to re-enter the cut in this much lower position, which naturally would lead to broken tooling, destroyed fixturing and ultimately public drunkeness. :p

So first the lock must be set tight enough to keep the assembly from falling down, and then the feed force clutch must be adjusted tight enough to overcome this resisting force but not too tight as this would then lead to the destruction of the "hard stop" that I had previously described. Which I am sure is what caused some of the parts to become missing on my machine, as that worm drive arrangement would tend to make mince meat (mince steel?) out of whatever worm wheel (mince bronze???) it was driving. It was not the best design in that it would be so easy to make it self destruct, but I guess I haven't thought of a viable alternative so maybe I should shut up about that.

The whole assembly of the clapper block and feed slide is a deceptively complex assembly to allow for power feed in addition to varying the angle of traverse and varying the angle of swing of the clapper block. I can't quite imagine how they went about integrating the radius cutting function as Old Hat and one of the advertisements that Russ linked to suggests. It must have looked something like a milling machine set up to do helical milling or differential indexing.


Old Hat
09-08-2014, 11:30 AM
A I can't quite imagine how they went about integrating the radius cutting function as Old Hat and one of the advertisements that Russ linked to suggests. It must have looked something like a milling machine set up to do helical milling or differential indexing.


The "punch-shaper" was gone before I was on the seen. It's usefullness was described to me by two individuals
neither of which I fully grasped. I've never put the apparatice that goes with the Gemco on the machine.
A friend of mine lost the beautifull manual Gemco put out, that goes over the workings of the head-feed option.
For a while the same manual was on Ebay buy over $45 so I let it be.

I found a Steptoe which had partialy self-distructed by over-feeding but soon went into heavy overtime
and that was the end of that. I still have the clapper box nearly unused.
Sorry, I wish I had this one in the bag but I don't.

Mister ED
09-08-2014, 06:39 PM
I don't know the answers to your questions ... but dang that thing is pleasing to the eye. Any idea what the vintage is?

09-09-2014, 12:16 PM
I don't know the answers to your questions ... but dang that thing is pleasing to the eye. Any idea what the vintage is?

I wouldn't know the date for my machine but the ad that Russ linked to is 1919 and the original patent dates are 1901.

My machine looks nearly identical to the one in the photo which looks very similar to the one in the ad, so I suppose it would be safe to speculate that these machines were made anywhere from 1900-1940?