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jbacc
08-22-2014, 11:17 PM
Hi All,

I am refurbishing an old B&S Dividing head and a split plate on the side near the crank is held in place with four flat head slotted machine screws. The heads on three of the screws have broken off and I was able to get them all out. The problem seems to be that these are not standard size screws.

The screw mics out around .183 which is the approximate size of a #10 screw but my pitch gauge and my tired eyes show it to be 40 TPI. The head on the one remaining good screw does not seem to be as large as a standard machine screw either. In any event, would anyone know of a source for these uncommon machine screws? I am guessing I might have to tap the holes in order to use a more common screw if I cannot find replacements? I sure would hate to do that...

Many thanks to all,

Joe...

andywander
08-23-2014, 12:51 AM
Not sure where you could get the screws, but why not make them? If you don't want to single-point them in the lathe, JTS has a die for less than $10.

http://www.jtsmach.com/jtswebshop/Taps_Dies/T125.asp

macona
08-23-2014, 12:57 AM
10-40 might be used in gunsmithing.

jbacc
08-23-2014, 01:12 AM
Thanks, it seems making my own might be my only option.

jbacc
08-23-2014, 01:13 AM
10-40 might be used in gunsmithing.

I thought the same thing and checked Brownell's and almost every other hit in Google. Looks like I will have to make my own...

Thanks for your help,

Joe

dp
08-23-2014, 02:42 AM
It's fun, too. http://metalworkingathome.com/?p=40

David Powell
08-23-2014, 05:30 AM
It's fun, too. http://metalworkingathome.com/?p=40

Many who build small model steam engines use 40 tpi taps and dies to make small fittings, 3/16" by 40 tpi is a common thread. beware, they are available both in 55 degree ( Whitworth ) or 60 degree( North American) thread form. Many model makers suppliers stock them. The two thread forms CAN be made to fit each other by very slightly squeezing in split dies, thus producing slightly undersize male threads, not correct in theory, but a quick answer for a hurried repair. Hope this helps David Powell.

jbacc
08-23-2014, 08:28 AM
It's fun, too. http://metalworkingathome.com/?p=40


DP, Thank you, very informative and I do appreciate it.

Joe

jbacc
08-23-2014, 08:29 AM
Many who build small model steam engines use 40 tpi taps and dies to make small fittings, 3/16" by 40 tpi is a common thread. beware, they are available both in 55 degree ( Whitworth ) or 60 degree( North American) thread form. Many model makers suppliers stock them. The two thread forms CAN be made to fit each other by very slightly squeezing in split dies, thus producing slightly undersize male threads, not correct in theory, but a quick answer for a hurried repair. Hope this helps David Powell.

Hi David, it is very helpful.

Thank you,

Joe

ammcoman2
08-23-2014, 09:14 AM
Recently bought a 3/16-40 tap and die from PM Research http://www.pmmodelengines.com/shop/tools/straight-pipe-thread-taps-dies/

Very good quality.

Geoff

jbacc
08-23-2014, 09:17 AM
I thought some photos might prove to be helpful.


http://JoMar.zenfolio.com/img/s6/v138/p570081701-2.jpg (http://JoMar.zenfolio.com/p346960610/e21fac1a5)



http://JoMar.zenfolio.com/img/s6/v151/p735244678-2.jpg (http://JoMar.zenfolio.com/p346960610/e2bd2f186)

Bob Fisher
08-23-2014, 11:24 AM
Why not go to Brown & Sharp? They, and Lufkin Are very good with replacement parts. Four screws shouldn't cost too much. Bob.

Toolguy
08-23-2014, 12:02 PM
Brownell's also has screw blanks so you can put your own threads on them. That way you can just turn to size if needed, thread and you're done.

Cuttings
08-23-2014, 12:46 PM
I just found a sight that might be a source of good information on this subject.
<http://www.efunda.com/designstandards/screws/unified.cfm>
It lists a 10- 40 UNS thread and gives all the specs. for it

Paul Alciatore
08-23-2014, 03:07 PM
From a web search for "machine screw 3/16-40":

http://www.adelfastener.com/
http://www.adelfastener.com/customer/C000507/20131132254076570.pdf

About 1/4 down the page they list 3/16-40 (3/16 = 0.1875")


These guys have then, but you gotta buy a few:

http://www.shamrockexpress.com/screws-machine-screws-pan-head-phillips-machine-screw-steel-zinc-0503mpp.html

Perhaps they could supply the name/address of someone who has purchased them and who would sell smaller quantities. Or perhaps you could ask for samples.


A search for "machine screw 10-40" also brought many returns.

CCWKen
08-23-2014, 06:05 PM
I'd just run a 10-32 tap in and be done with it. Sometimes you guys just make it harder than necessary. ;)

It's not like the thread police are going to check your restoration.

David Powell
08-23-2014, 08:11 PM
I'd just run a 10-32 tap in and be done with it. Sometimes you guys just make it harder than necessary. ;)

It's not like the thread police are going to check your restoration.

Rethreading a 40 tpi thread with a 32 tpi tap will work BUT you lose some strength because a portion of the thread will be missing. IF the length of engagement is fairly long relative to the diameter of the thread then the loss is probably totally insignificant, the screw will likely break before the threads strip, BUT if the length of engagement is small, say only 2-3 times the diameter of the screw then there is more likelihood the thread will strip. Those who are mathematically inclined can work it out for us. I like at least 5 turns of engagement as a minimum on good threads and a lot more if on a rethread such as this. Regards David Powell.

JCHannum
08-23-2014, 08:39 PM
While the 10-32 tap may or may not work rethreading the existing holes, there is nothing wrong with rotating the index plate 180 degrees and drilling and tapping three new 10-32 holes. That will work and will solve the problem that will occur in the future when changing the plate and losing one of the screws under the bench.

andywander
08-23-2014, 11:49 PM
Good point-a 3/16" is .1875, while a #10 is .19-close enough that it should work just fine.

Rich Carlstedt
08-24-2014, 02:10 PM
Joe
My B & S Dividing head which is from about 1890-1900 has 12-32 screws.. FYI

Rich

krutch
08-25-2014, 03:56 PM
Have you tried Micro Fasteners? Their order site is www.microfasteners.com
I don't know where they start & stop as to size or thread.

Ron of Va
08-26-2014, 07:32 PM
I have never seen a 3/16 screw, they must be pretty rare. Are you sure it isn't an M5?

I use this chart when I am trying to sort or identify screws. I find it real handy.
http://www.hunt101.com/data/500/medium/BoltIdentification1.jpg

jbacc
08-26-2014, 08:53 PM
I have never seen a 3/16 screw, they must be pretty rare. Are you sure it isn't an M5?

I use this chart when I am trying to sort or identify screws. I find it real handy.
http://www.hunt101.com/data/500/medium/BoltIdentification1.jpg

Hi Ron,

Thanks for posting the chart, I will save it. Unfortunately, M5 does not work..... Looks more and more like I will have to make the screws. Retapping to a more common size and using helicoils are also an option.

Thanks to everyone for you help and assistance.

Joe

jbacc
09-01-2014, 05:13 PM
We'll, after lots of searching, I took the advice of some and made my own screws. They turned our ok and are installed on my B&S dividing head. Many thanks and much appreciation for everyone's help and guidance.

Regards,

Joe