For interest - How were fly-presses made ?

[Overland]

I was thinking about a flypress recently, and it took me back to my time as a kid working Saturday mornings at a little shop, and using a flypress to make brackets and the like.
This type of presses uses a multi-start "square" thread to create the force.
I can see how the thread on the "bolt" could be made on a lathe, but the "nut" seems to be machined directly into the casting, I think.
These are pretty massive screw threads being perhaps 3" diameter with thread grooves certainly 1/4" deep.
I can't get my head round a tap that size; nor how you would "single point" it in a vertical mill.
These presses were mass produced back in the 18 th century, so nothing too sophisticated.
Maybe it was a bushing.
I'd be interested if anyone knows.
Bob

In the image below, the "nut" is in the frame above the scewthread showing, and the block below the thread holds the tool.

 

[Overland]

Another, better image.

 

[memphisjed]

Rifling buttons.

 

[sfriedberg]

Taps were definitely possible. Decent cast iron is pretty easy to cut, and doesn't produce long curling chips. I've seen buckets of 1.5-2.5" diameter carbon steel taps from 75 years ago. On a job like this, I'd imagine a series of taps would be used to gradually enlarge the major diameter of the threads.
But in mass production, I suspect these were made on a machine with guided motion, not a pair of grunts using a pipe cheater on a fat multistart tap. Think helical broaching. Given the small base hole and limited space under the head of your 2nd photo example, multiple tools were still probably used.
[Added in edit] Helical broaching works like the rifling buttons memphisjed suggests.

 

[magneticanomaly]

Single-point in a lathe....workpiece does not have to be small or cylindrical
Broach in a slotter with helical tool guide
Cast babbitt or even bronze around a mandrel
Special long progressive tap, or set of taps as can be bought form stock for single-start Acme threads
Probably lots of other ways.

 

[Overland]

Can't imagine swinging a 750 lb casting so far off center on a lathe !
I just googled Acme taps and found a 2-4 at MSC at $700; surprised me they're available.
So I guess a "Very Special Order" tap could be a way of doing it.
Would need a big-ass radial arm drill to drive that sucker !
Fascinating.
Any of you old Brits know ? lol
Bob

 

[stephen thomas]

My brother has had and rebuilt them
The big one i remember more clearly was simply poured babbitt.
Which he removed, set up and re-poured.

I think that was common 19th c technology.

Smoke the screw thoroughly, and make sure it is centered, and fixtured dead straight both ways. Dam it well at the bottom.
Can't recall is he used one, but for a thorough pour in something like that without could shuts, a riser or 2 can be useful.

I'm not up on babbitt, but there are different metals that go by that name. (even if not original formula) so pick one that is high strength, to add to the stuff you knock out to melt and re-pour. Be sure all the keys in the casting are cleaned out, so it locks in well.

smt

 

[FamilyTradition]

Not entirely uncommon to see taps in that size and above (for example, 2-inch pipe taps are still routinely used in some applications). As others have noted, could have been a tap with a long chamfer or a set that progressively got bigger in P.D. until the final size.

 

[fciron]

All of mine have a separate nut, some are retained by a threaded ring which is recessed into the top of the casting (outside of the ring is threaded). I don’t recall if there are any other systems but it seems like it would be pretty easy to put a flanged nut in from below and then secure it with a set screw or pin to prevent rotation.

 

[magneticanomaly]

A separate nut, an easily made and easily replaced wear-part, makes the most sense.

 

[john.k]

Ive seen big fly presses with two threads on the screw......coarse acme ,and a superimposed finer thread ,say 8 tpi...........never used a fly press ,but wondered what the finer thread was for.

 

[sfriedberg]

I'm going to guess the finer thread was for a travel stop. I can't see how both threads could possible act on the same nut simultaneously.

 

[Asquith]

Yes, the fine thread is for a travel stop.

 

[jaco1]

The internal thread in old post vices was made by wrapping the external thread with a rod, and brazing the rod in place. This wont work for a double lead.
I expect a sleeve was turned on a lathe. The either shrink fit, or brazed in place.

 

[fciron]

here’s three pictures of fly press “nuts” in my shop. The blue one is an Adams, the other two are unmarked. Pretty sure they’re all American.

The nuts are all separate and put in from the top. You can see the holes for a spanner in the two black ones.

You can see the depth stop on the fine threads of the Adams. It’s reverse threaded so that when it handles hits it it locks up solid because the rotation of the screw traveling downward makes the stop travel upwards.

https://flic.kr/p/2nyMjUt
https://flic.kr/p/2nyKWiL
https://flic.kr/p/2nyEN9A

 

[fciron]

Eh, you can’t actually see the depth stop, here’s a better picture

https://flic.kr/p/2nyMtYA

 

[Overland]

Thanks fciron.
So you think the nuts are screwed in to the casting. Interesting.
Bob

 

[Overland]

I was thinking how you'd cut those screw threads.
Looks like a four start thread with a pitch of maybe 2".
My Colchester 21x80 late has a max thread pitch of 2 tpi. Would need to do quite a bit of work to the gear train to that sort of pitch. I wonder if I could even get big enough gears in there.
Just musing for interest,
Bob

 

[fciron]

If you were in the Flypress business it would be an easy call to invest in a special setup to cut the thousands of nuts you’d need.

I’d probably do some sort of live tooling and cut the thread in a single pass. The angle is steep enough that broaching is a possibility especially if there was positive control over the rotation. (I saw an old timey/reenactor gunsmith do something similar for rifling barrels.)

Edit: The more I think about it with my mass production hat on, the more I like broaching.

 

[fciron]

Something like this, but metal and industrial