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markrob
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Weekend Project Making a Presto 6N Lead Screw

Post: # 4310Unread post markrob
Sun Feb 01, 2009 11:12 am

Hi All,

I was looking for a shop project this weekend and decided to tackle making a new lead screw for my Presto 6N. I have a small 6" Craftsman metal lathe and an import micro mill, so I thought I could handle it. It took some time, but the end result came out very nice. I decided to make a 160 TPI screw since I have 96 and 224 TPI already. Here is a simple drawing of the dimensions I was able to read using my exisiting screws.

http://home.comcast.net/~markrob1066/docs/PrestoScrew.pdf

Note that the depth of the thread will depend on the pitch. In the case of the 160 TPI, I stopped at .030". That seems to work fine for this pitch.

Here is a picture of the completed screw.

Image

If anybody is interested, I can give you some tips on how to machine one. Keep in mind I'm no master machinist. I'm sure a real pro could knock this out in no time.

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cd4cutter
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Post: # 4312Unread post cd4cutter
Sun Feb 01, 2009 4:08 pm

Nice looking piece, markrob. I'm not very experienced with machine tools, so I may be asking some dumb questions, but here goes: What material did you use - mild steel or tool steel? What kind of cutting tool did you use - steel or carbide? How did you cut the .0625" slot in the end of the piece? Do you plan to harden this part or is it hard enough already?
Collecting moss, phonos, and radios in the mountains of WNC

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markrob
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Post: # 4319Unread post markrob
Mon Feb 02, 2009 7:48 am

Hi,

Thanks for the feedback!

I used 12L14 steel which is known as a free maching steel. Its easy to work with and takes a nice finish. I don't plan on hardening since I doubt there will be much of a wear factor. Besides, I can always make a new one of this wears. To cut the butress thread, I ground a form tool by hand using a high speed steel blank. Took a bit of time to get this close, but its not that critical in terms of the angles. I just needed to be sure I left plenty of clearance on the front and sides of the tool. Because of the 90 degree wall of the thread, you have to advace the tool directly into the work instead of the normal 29 degrees. This makes it a bit tougher to cut the threads. I just took small passes till the job was done. When the screw was complete, I removed it from my lathe, clamped it in my milling vise, and used a 1/16" end mill to rout the key slot. I'm sure if I do it again, it will go much quicker and the result will be more accurate, but I was very happy with the results.

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VRCM
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Post: # 4321Unread post VRCM
Mon Feb 02, 2009 9:54 am

Normally you would case harden it, right?. That is not the easiest thing to do.
Tim

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markrob
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Post: # 4324Unread post markrob
Mon Feb 02, 2009 1:27 pm

VRCM wrote:Normally you would case harden it, right?. That is not the easiest thing to do.
Hi,

I'm not sure how I would attempt to harden the leadscrew. I've never tried to do this with any of my metal working projects. If I had to guess, I would think that using water or oil hardening type drill rod would be the easiest to do on a DIY basis.

Mark

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VRCM
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Post: # 4325Unread post VRCM
Mon Feb 02, 2009 2:46 pm

Yeah. Plus you might run the risk of warping the screw.
Tim

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piaptk
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Post: # 7392Unread post piaptk
Sat Jan 16, 2010 1:04 am

So, I'm a little hazy on the geometrical conceptualization, but, if you reverse the direction of the grooves on one of these (assuming you have it machined with this in mind) can you do inside out without adjusting the motor on a 6N? i'D love to do inside out grooves, but thought I'd have to reverse the motor.

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mossboss
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Inside out cuts

Post: # 7395Unread post mossboss
Sat Jan 16, 2010 1:49 am

Hey
It is quite simple one is a normal thread like screw clock wise the other is a left hand thread
You start the cutter engaging thingy from the inside close to the centre and it winds it out to do an inside out cut
The converse takes place with normal cuts start on the outside screws it inwards
No need to reverse the motor man Think about it The record still has to spin clockwise so as to play Ha Ha
Cheers
Chris

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fraggle
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Post: # 7400Unread post fraggle
Sat Jan 16, 2010 3:34 am

this material would bend if you harden it. every steel bends if you harden it. i think the only way to get a very accurate hard thread is to harden it and to grind it afterwards which that means.
- machining and cutting the tread (not finished)
- harden the material
- machining it again (finishing)
or you could finish it and have some sort of surface hardening or powder.
i don't know exactly how to say that in english but there is a way with powder so just a very thin layer which is hard.
i reckon you should be fine without hardening this screw..
just don't use mild steel..

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mossboss
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Screws

Post: # 7401Unread post mossboss
Sat Jan 16, 2010 4:49 am

Hey all
These things where never hardened
They where turned on a screw cutting lathe at very low speed and a sharp tool
There is no need for them to be hardened they do not do much work really for the size they are made out off
The Presto ones are around 3/4 " to move a head at around 1 LB mass
The Neumans are even bigger
Besides they where made out of ECN 150 or a W301 steel which are tool grade steels and quite tough
Any good quality tool steel will do the job
If any one wants the "ants pants" they can get the thread ground with an already hardened rod stock which is a waste of money and effort
Just about any micrometer sold in the market has their threads ground on very tough chrome steel
But than again as I said why would you bother
You will never wear one of them out regardless how many cuts you do
A living example are the prestos scullys Neumans and all of the lathes that are still in use today
Never heard of one needing a screw change due to wear
Rusted out damaged due to being dropped different pitch yes wear out NO
Ah I nearly forgot Keep them well lubricated with a few drops of oil
Singer Sewing machine oil is great stuff, cheap available everywhere
Cheers
Chris

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Steve E.
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Re: Weekend Project Making a Presto 6N Lead Screw

Post: # 22814Unread post Steve E.
Fri Jan 25, 2013 11:07 am

I've moved this one to "Schematics."

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