2 start thread on fountain pen

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2 start thread on fountain pen

This topic has 5 replies, 4 voices, and was last updated 15 September 2010 at 22:37 by steve kendall 1.

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15 September 2010 at 09:49 #55664
steve kendall 1
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@stevekendall1
Hi

I have lost the cap for my stainless steel fountain pen and I am trying to make a replacement. As near as I can measure the thread seems to be square form, major diameter 12.7 mm, minor diameter 12.1 mm, pitch 1.6 mm per rev. number of starts 2.

I have read Screw cutting in the lathe, and found it nery helpful.

I have ground a HSS tool 0.4 mm wide, and cut an internal thread on a piece of scrap brass. This almost fits, but does not run freely. Does anyone have any advice, particularly on measuring and identifying the thread form?

I am using a SEIG C4 lathe using 16 TPI screw cutting feed, and I move the compound slide 0.8 mm to make the second start. I have made a tap from silver steel and hardened it but I am having difficulty using it to cut a thread, I think because it is square form.

Can anyone help?

Will anyone with cutting threads be at the Myford open days so I could show you my problem and efforts so far?

Regards

Steve
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15 September 2010 at 09:49 #5184
steve kendall 1
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@stevekendall1
15 September 2010 at 10:28 #55665
ady
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@ady
This is a handy site for threads.

http://homepages.tesco.net/~A10bsa/bago.htm

Searching on fleabay can also help find weird stuff which may be relevant.

http://cgi.ebay.co.uk/1-2-X-16TPI-BSF-Tap-DALZEN-/180559718479?pt=LH_DefaultDomain_3&hash=item2a0a32a84f

Edited By ady on 15/09/2010 10:41:35
15 September 2010 at 13:32 #55675
Clive Foster
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@clivefoster55965
Steve

Starting with the obvious are you sure that the thread is 1.6 mm pitch rather than 16 tpi, the two are very close and will be hard to separate using a normal thread gauge on a square thread. Difference is just enough to prevent smooth running.

Normal practice with square threads is to make the tool a fraction narrow and feed longitudinally once the thread is down to depth to clean out the corners and get clearance.With two start threads its a right pain figuring out which start is at fault if things don’t fit.

Might be worth doing a single start properly after clearing out the space occupied by the second start so you can play about with things and sort out exactly what settings are needed to get the thread right. Once you know what’s going on its not too hard to transfer relevant details to the real job.

That’s a very small thread so its hard to see what you are doing. May be quicker all round if you do a practice run at a size and pitch you can easily see. Say 1″ diameter. Use friendly material too, delrin is ideal if you have it.

Generating the offset by moving the compound always seems error prone to me, especially on a baby thread. Given the choice I’d shift the spindle through 180°.

Clive
15 September 2010 at 21:45 #55697
Sub Mandrel
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@submandrel
Steve,

If it doesn’t quite work (e.g. it’s 1/16″ rather than 1.6mm) you could just try only having a small number of threads and having alarge runout groove. (OK ,it’s a bodge but…)

Neil
15 September 2010 at 22:37 #55702
steve kendall 1
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@stevekendall1
Hi Neil

That’s a good idea, it will solve my problem and I can start using my pen again!

Thanks

Steve
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