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Need to make a nut for this odd size 250 year old bolt

rivett608

Diamond
Joined
Oct 25, 2002
Location
Kansas City, Mo.
I need to make some jam nuts for these bolts from an 18th c. English lathe I’m restoring. It is about .415 x 12 tpi. Note the rounded profile of the threads, also the head is octagon. In all my taps I don’t have that one, closest is a taper tap with the small end at .400, I don’t think it will start cutting anywhere near that size.

So how would you do this? I figure option one is to make a tap or option two, grind a cutter and thread the hole on the lathe. Btw, I’ll be doing this on a 1968 vintage lathe. It is the newest I have and 200 years more advanced than the lathe the maker of this had. Think what he would have thought if he could play with that?

How would you do it, and please no CNC stuff ideas because I don’t have that stuff.

Thanks
 

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I assume the lathe you are restoring has no back gears etc as those appeared circa 1800

All screws and nuts of that period would be hand fit and prior to any standardization of thread forms.

I would grind a tool as best as I could to match the thread form and try it at 12 TPI, although the individual screws will probably vary from one to the next
 
If a 12 TPI fits good you can use the screw for a gauge to make a HSS tool bit boring bar and with care cut/bore 2 or more nut depth into some hex stock...then part or hack saw then off.

Yes need a thread cutting lathe, or have a feed per rev of about .083".
 
Ha that looks a heck of a lot like threads I see on old clocks and watches (but bigger). I say make a tap, it would be easy enough to make a form tool to match the thread, O1, tap doesn't have to be fancy, just grind 3 flats on it and taper the business end. I've seen a lot of old production taps that were as simple as that.

Earlier this year I had a request for a series of parts with a left hand thread in it and didn't have the tap on hand. I really wanted to do a proof piece before quoting a hard price. Found a screw with the correct left hand thread, rehardened it, ground 3 flats and made a simple die, then simple tap, all went really fast like maybe an hour (ok it's a 0.7mm thread so I wasn't hogging any stock or heat treating in ovens). Made the quote and got the thumbs up same day the real taps came in.
 
I would single point thread the nuts since you only need two. If you want to send me the bolt, I will make you two nuts out of wrought iron so they are authentic. I recently made some wrought iron bolts for an Otto & Langen engine that were .515" OD and 11.94 TPI.

The bolt head is octagonal, but I suspect the nuts were square. But how could one know for sure? Would octagonal nuts look better or make more sense for adjusting jam nuts? Probably need a pair of hand forged wrenches, too.

The picture of the old bolt looks like it has an axial forging or rolling seam.

Larry
 
I'd screw cut it, ....Yes I know it's old etc etc ----------so at the risk of being labelled a vandal, helicoil the hole in the late to 7/16UNC or Whit and make a bolt to match.
 
Interesting, in thinking about what shape the jam nuts should be on the outside I looked at the bolts. It appears the original jam nuts were chilled off. I might do sort of a disk with a spinner hole that would look the most like a few of the other fasteners on the lathe. If they were kind of thin with small holes they could have easily stripped hence the need to chilled away. The 8 sides On the heads appear to be filed.

Here are some more shots of the bolts.
 

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The obvious way at least to me would be to single point thread if you can match the lead.
I would grind a tool from an off the shelf carbide ID grooving tool. An optical comparator or tool makers microscope would make life easier when grinding the tool. I’m assuming you have good magnification in your shop. I’d also look at the fit of the root of the thread with a pin gauge so you have something to compare to.

Ps, it was good to meet you at the last Handworks in Amanda, I had planned to go to this years event before the cancellation was announced.
 
I have worked on many English and American 18th century clocks and have found that BA threads usually are the closest fit. Before thread standardization, a clock shop would use a screwplate to make screws and taps. My belief is that BA threads are based upon the old Stubbs screwplates which would explain the similarity.
 
Think in terms of a machinist in the 18th century and how they cut threads. Screw cutting lathes were either non-existant, or very rare (depending on time period). A machinist would have cut the threads in a very simple lathe without benefit of lead screw, change gears, or even a slide tool rest. They may have roughed the thread out using a single point tool and establishing the pitch of the thread by eye/experience and maybe some chalked lines on the work to set off the pitch of the thread. They may also have had a multiple-point cutting tool which was filed out of flat tool steel and had more precise pitch and form. Either tool was used on a tee rest.

Internal threads were cut in much the same manner, with a single point tool having a 90 degree bend between the shank of the tool and the actual cutting section, and the same sort of multiple-point tools adapted for internal threads were used.

Taps and dies were often made by individual machinists using these same methods for cutting the threads on them. The result is the pitch of a thread cut by these methods may approximate a 'regular pitch' such as a lathe or tap or die would cut. Thread form was also a non-standardized thing in those times, maybe a larger shop might have set their own standards for form and pitch, but there was no across-the-board standardization.

My thinking would be to grind a form tool- my own preference is to use high speed steel- and try to match the thread form on the bolt. Not everyone has access to optical comparators. Thinking like a machinist of olden times, I'd likely get a piece of thin steel and file a thread template gauge, using the threads on the bolt as the 'master'. With a magnifying glass and some careful filing, a template gauge could be filed out. The tool bit for cutting the threads is then ground and stoned to match this template gauge.

I'd grind two tool bits- one for cutting male threads, and a small boring bar for cutting the internal threads. The external threading tool is mainly to check your work. I'd cut a sample external thread and try it against the original bolt as a kind of 'thread profile gauge'. This will tell the tale as to whether the lathe is cutting a pitch that matches, or very nearly so, the original bolt.

Chasing a thread using a graver or multi-point tool is something I've only read about. Never seen it done, let alone have I done it myself. Back in the day, this was a skill many machinists developed. I wonder if anyone is still amongst the living who can cut accurate screw threads by these old hand methods. As for the class of fit of mating threads cut by these methods, it was probably all over the board and varied with the skill of the machinists. Taps and dies made by these methods might actually have had a better chance of getting a closer fit if the tap was used to cut the internal threads in the die when it was being made.

We take so much for granted at every level of our lives. Lathes with quick change gear boxes for threading and feeds are almost universal, while the 'loose change gear' lathes are mostly antiques or relegated to home shops. Most people who operate lathes have likely never had to make up change gears to cut a particular thread.

Every so often in my engineering practice, a job will come along to do some design work for either the repair or re-creation of some historic old mill or machinery. I get told: "Think like 1840 (or 1890)" or whatever era the original mill or machinery was from. It's an interesting exercise to write off using welded fabrication (or at least none that is visible), designing cast parts, and avoiding the use of vertical milling machines. The job Rivett608 has posted about is one of those jobs that put me in that 'think like the 18th century' mode. I am lucky: the historic engineering work I get into is usually from the late 1800's, and is big enough and 'loose enough' that methods such as blacksmiths and millwrights used are close enough. Matching a smaller screw thread, let alone a female thread, is a good deal tougher than anything I've tangled with.

Hopefully, a standard pitch of thread that a lathe can cut will match up close enough.
 
Thanks Joe, you explained my thought better than me. I have been thinking about this from an 18th c. perspective. The first thing I did was check my stash of 18th and early 19th c. taps and dies. I have quite a lot but since I do miniatures I had nothing that big. If it was an outside thread I would hand chase it as I have done before.

I think I’ll just grind a HSS bit to the profile and thread it on the lathe.

I had wished I had a period tap the right size, they are fun to use and so different from a modern one.

Here is what I have, my hand chaser for inside threads was for working in bigger hole and this early tap is just a hair to big. Btw, it seems to be as close as an 18th c. Machinist could get to 12 tpi.
 

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An epoxy mold of the bolt threads, using a release agent, (WD-40) will produce an accurate guide for grinding a form tool. I used an optical comparator for years, but my Opti-visor works.
 
Going a bit on what Joe was saying about chasing threads. I didn't know this was even a thing until 20 some years ago when an English clockmaker told me about woodworkers chasing threads with a handheld tool (I was a snot nosed 25yo, c'mon). Blew me away. I swear he said the ancient guys did it on metal too but was maybe just my wonderment at the time.

Wouldn't try it on this, especially with a lathe at hand that can do the pitch.

MrStretch reminded me I should seek out some Stubbs screwplates. All mine are Martin or German.
 
.415 dia at 12 tpi would about 13* helix so one might mark 12 lines at the OD surface. mark another 12 lines half way between at a half turn 180*, then with file at 13* file x number of strikes and file-go-round the part of a would be screw.

Yes lay a wire in the thread to look over(eyeball) to be sure it checks 13*.
 








 
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