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Posted by Matthew Zenkar on April 13, 2006, 12:27 am
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Please pardon me if this is not the correct forum for this message.
I am working on a design that I think is best described as a precision
positioning assembly for optics. I contacted a professional gear
designer, and I was told by this person that the design would be
improved if I used an acme thread for the threaded rod that is in the
assembly.
My initial design called for a 3/8"-40 thread as this is the finest
standard thread size I could find to fit a 3/8" diameter rod. However,
looking in Machinery's Handbook, I found that the finest standard acme
thread is 1/4-16. I also figure that I would be able to use a 20 pitch
with another minor adjustment in the assembly.
Is it common practice to have custom threading made for those cases
where standard threads do not meet the needs of a project? For my
case, I would like to have acme threaded parts where the thread size
is 3/8 or 1/2-20, more preferably, 3/8 or 1/2-40.
Also, if it is not heard of to have acme threads custom acme threads
made in those particular sizes, what about having what Machinery's
Handbook calls "unified screw threads" cut to a non-standard size, say
1/2-40 - is this done for cases where standard threads do not meet the
needs of a project?
Also, does anyone have any recommendations as to where I might get
this done (preferably by a professional shop)?
Thanks in advance for your response.
Best Regards,
Matthew
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Posted by Voltes34 on April 12, 2006, 11:46 pm
Please log in for more thread options
| Please pardon me if this is not the correct forum for this message.
|
| I am working on a design that I think is best described as a precision
| positioning assembly for optics. I contacted a professional gear
| designer, and I was told by this person that the design would be
| improved if I used an acme thread for the threaded rod that is in the
| assembly.
|
| My initial design called for a 3/8"-40 thread as this is the finest
| standard thread size I could find to fit a 3/8" diameter rod. However,
| looking in Machinery's Handbook, I found that the finest standard acme
| thread is 1/4-16. I also figure that I would be able to use a 20 pitch
| with another minor adjustment in the assembly.
|
| Is it common practice to have custom threading made for those cases
| where standard threads do not meet the needs of a project? For my
| case, I would like to have acme threaded parts where the thread size
| is 3/8 or 1/2-20, more preferably, 3/8 or 1/2-40.
|
| Also, if it is not heard of to have acme threads custom acme threads
| made in those particular sizes, what about having what Machinery's
| Handbook calls "unified screw threads" cut to a non-standard size, say
| 1/2-40 - is this done for cases where standard threads do not meet the
| needs of a project?
|
| Also, does anyone have any recommendations as to where I might get
| this done (preferably by a professional shop)?
|
| Thanks in advance for your response.
|
| Best Regards,
| Matthew
Given the same amount of tolerance, the finer the thread pitch the more
precise the movement.
The diameter of the rod is really not a critical factor.
|
|
Posted by Harold and Susan Vordos on April 12, 2006, 11:53 pm
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> Please pardon me if this is not the correct forum for this message.
>
> I am working on a design that I think is best described as a precision
> positioning assembly for optics. I contacted a professional gear
> designer, and I was told by this person that the design would be
> improved if I used an acme thread for the threaded rod that is in the
> assembly.
>
> My initial design called for a 3/8"-40 thread as this is the finest
> standard thread size I could find to fit a 3/8" diameter rod. However,
> looking in Machinery's Handbook, I found that the finest standard acme
> thread is 1/4-16. I also figure that I would be able to use a 20 pitch
> with another minor adjustment in the assembly.
>
> Is it common practice to have custom threading made for those cases
> where standard threads do not meet the needs of a project? For my
> case, I would like to have acme threaded parts where the thread size
> is 3/8 or 1/2-20, more preferably, 3/8 or 1/2-40.
>
> Also, if it is not heard of to have acme threads custom acme threads
> made in those particular sizes, what about having what Machinery's
> Handbook calls "unified screw threads" cut to a non-standard size, say
> 1/2-40 - is this done for cases where standard threads do not meet the
> needs of a project?
>
> Also, does anyone have any recommendations as to where I might get
> this done (preferably by a professional shop)?
>
> Thanks in advance for your response.
>
> Best Regards,
> Matthew
Acme threads are generally restricted to rather coarse pitches-----so you're
highly unlikely to be successful in your quest to use 1/2"-40.
Standard 60 degree threads (the unified thread series) are generally
selected for your application, and are available in pretty much any
pitch/diameter combination you desire. Bastard, or non-standard, taps are
readily available from supply houses, but should you elect to go with
something that is considered unusual, or non-standard, you can have taps
made for a reasonable price. You should be able to buy a 1/2"-40 tap with
no trouble.
The nature of your device may dictate the need for a ground thread.
Threads can be generated by various means, from cutting with a die, a die
head, rolling, single point threading on a lathe, or grinding. I may
have even left out some other method. It might be helpful to know more
about your thread requirement before suggesting a system that would be in
keeping with your requirements. Are you looking for one, or many? How
long must the thread be? What material? Considering you are using the
thread for adjusting, or locating, you may even wish to consider threads
without lash, or clearance.
Harold
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|
Posted by James Waldby on April 13, 2006, 1:50 am
Please log in for more thread options Matthew Zenkar wrote:
> I am working on a design that I think is best described as a precision
> positioning assembly for optics. I contacted a professional gear
> designer, and I was told by this person that the design would be
> improved if I used an acme thread for the threaded rod that is in the
> assembly.
>
> My initial design called for a 3/8"-40 thread as this is the finest
> standard thread size I could find to fit a 3/8" diameter rod. However,
> looking in Machinery's Handbook, I found that the finest standard acme
> thread is 1/4-16. I also figure that I would be able to use a 20 pitch
> with another minor adjustment in the assembly.
...
You haven't told us why the "professional gear designer" believes
an acme thread would be better. Whether that is so depends, of
course, on what your device has to do. Acme threads are used in
several places on lathes, for positioning things accurately and
solidly. You might be able to buy an assembly to do what you want;
eg search for compound slide on ebay to see items like
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7609388048
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=8923903725 and
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7607673342
(The first item has a 1/4-20 thread, not acme)
If the optics are lightweight, you might be better off adding a
DRO to your device and keeping the 3/8"-40 thread. See examples
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7606647083
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7606532048 and
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7606892197
and other items in same categories.
-jiw
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|
Posted by Richard J Kinch on April 13, 2006, 3:18 am
Please log in for more thread options Matthew Zenkar writes:
> Is it common practice to have custom threading made for those cases
> where standard threads do not meet the needs of a project?
Absolutely. Instrumentation is full of it. A common example is filter
threads on cameras.
You seem to have settled a lot of design questions prematurely, as if you
hadn't considered aspects like backlash and thread pitch inaccuracy.
> Also, does anyone have any recommendations as to where I might get
> this done (preferably by a professional shop)?
I design and built a lot of finely threaded parts for optical applications.
http://www.truetex.com/
|
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>
> I am working on a design that I think is best described as a precision
> positioning assembly for optics. I contacted a professional gear
> designer, and I was told by this person that the design would be
> improved if I used an acme thread for the threaded rod that is in the
> assembly.
>
> My initial design called for a 3/8"-40 thread as this is the finest
> standard thread size I could find to fit a 3/8" diameter rod. However,
> looking in Machinery's Handbook, I found that the finest standard acme
> thread is 1/4-16. I also figure that I would be able to use a 20 pitch
> with another minor adjustment in the assembly.
>
> Is it common practice to have custom threading made for those cases
> where standard threads do not meet the needs of a project? For my
> case, I would like to have acme threaded parts where the thread size
> is 3/8 or 1/2-20, more preferably, 3/8 or 1/2-40.
>
> Also, if it is not heard of to have acme threads custom acme threads
> made in those particular sizes, what about having what Machinery's
> Handbook calls "unified screw threads" cut to a non-standard size, say
> 1/2-40 - is this done for cases where standard threads do not meet the
> needs of a project?
>
> Also, does anyone have any recommendations as to where I might get
> this done (preferably by a professional shop)?
>
> Thanks in advance for your response.
>
> Best Regards,
> Matthew