Thread: Impero II: the cousin of parting tool

Originally Posted by Michael G

Bryan, you of all people should know the size of my tool post - some time back I swapped some 19mm HSS blanks because they would not fit my post.

Oh yeah . Well if you're going to make one my suggestion is to make it direct mount (BXA dovetail). Then you'll have room for a nice beefy taper for the helix adjustment.

See, we're here to help.

Another thread cutting tool - this one spotted on eBay. An interesting thing about this one is that the thread cutting part is a solid stick, so sharpening is just grinding a layer off the end of the cutter.
$_57.JPG
The best bit though is that by virtue of the pivot on top, it looks like it can be adjusted for helix angle in both directions. The Impero that started this thread was nice in that respect but required special disc cutters. Something like this could use a straight length of tool steel (like an Eccentric tool holder) but be able to cope with helix angle. As the cutter is straight I guess with a little thought lengths could be made for WW threads as well as metric and perhaps even ACME at a stretch with the help of a SG.
Again, the down side of this holder is that the shank is 1" high - but the principle is interesting.

Michael

Hi Michael,

Did it find its way into your shed? If so, what are the extra parts in the box?

Much like Ifanger, but with a positive helix adjustment, though my Ifanger has positive tool height.

(for those that havent seen an Ifanger)
https://www.woodworkforums.com/f65/tangential-toolholders-plagiarism-136649
https://www.woodworkforums.com/attach...6&d=1373336257
https://www.woodworkforums.com/attach...7&d=1373336263
https://www.woodworkforums.com/attach...4&d=1373332195

Stuart

Originally Posted by Stustoys

Did it find its way into your shed? If so, what are the extra parts in the box?

As much as I would like to say I resisted temptation, I didn't. (I'm not sure I can use this tool by itself so I may have to modify a holder for it or as an alternative use it as a model for a custom made tool)
There were two up for sale and I bought one. The box has several slots in it and from what I can work out, the long one across the back is for an adjusting spanner, the shorter slots are for extra cutters and the thing that looks like a comb gone wrong is for tool setting I believe.
The Ifanger looks interesting as it seems to have an almost identical tool bit. The tool is coming from the US, so I'm not expecting it to be here soon (especially with the joys of the global shipping program). When it gets here I'll post some more pictures.

Michael

After seeing MichaelG's response I had a look at some bits I have been saving not fully knowing what there off and found that I have a Incert Off a P&W Threading Tool.


Keith_W

Originally Posted by Pete F

Michael I've never seen anything like that before. Apart from being able to be sharpened almost indefinitely, what's the idea behind that?

These used to be homemade, but were commercially available not long ago, like this one in my Swiss tooling catalog from 1999, an internal/external grooving tool:
Einstech1.jpg
Note that the disc tool can be attached axially at the left (external grooving), or radially at the right(internal grooving)!


Main advantages of this design, besides the ease of sharpening:

- The tool form can be very easily and accurately turned on a lathe. The one in the pic is for threading, but you can easily shape for parting too. Then just cut out a segment, harden, polish, and it is finished.

- The toolholder is very simple to make, too.

- The mounting with a center screw means either the cutting angle is variable, or the center height is adjustable, or both. Depending on users choice and/or materials need.

Originally Posted by Michael G

As much as I would like to say I resisted temptation, I didn't. (I'm not sure I can use this tool by itself so I may have to modify a holder for it or as an alternative use it as a model for a custom made tool)

Probably just as well.... Threading tools are form tools and every thread pitch has a different nose radius or flat... One cutter would only do one pitch thread, unless you are a hack like me and rough on a lathe and finish with a die...

Originally Posted by .RC.

Threading tools are form tools and every thread pitch has a different nose radius or flat...

I thought that was Whitworth only. Metric and Unified you can do what you like as long as you stay on the right side of the line

Stuart

Originally Posted by Stustoys

I thought that was Whitworth only. Metric and Unified you can do what you like as long as you stay on the right side of the line

That's how I do it too, and Whitworth as Richard suggests gets a run with a die to profile

Michael

Originally Posted by Stustoys

I thought that was Whitworth only. Metric and Unified you can do what you like as long as you stay on the right side of the line

Stuart

The flat on the nose of a UN or metric thread gets wider the more coarse the pitch..

With a correct shaped tool, you know how deep to take the cutting tool to get a good thread... If the tip is not right, say too pointy, you have to go deeper to get the correct thread depth, otherwise the mating part will not fit..

This is where thread wires and such come into play... I have done OD threads on the lathe where the female part could not be used to check the thread..

I had to use thread wires and they told me when the thread was cut deep enough... If I had some sort of device to closely look at the tool tip and be able to measure the flat it would make life easier at times....

Originally Posted by .RC.

The flat on the nose of a UN or metric thread gets wider the more coarse the pitch..

With a correct shaped tool, you know how deep to take the cutting tool to get a good thread... If the tip is not right, say too pointy, you have to go deeper to get the correct thread depth, otherwise the mating part will not fit..

But the size of that flat is a max(or min depending), in UN or metric you can't be any amount smaller(or a radius) and still be in spec?.
You can also radius the crest and still be in spec(though I haven't looked this up lately )

Stuart

Originally Posted by Stustoys

........
You can also radius the crest and still be in spec(though I haven't looked this up lately )

Stuart

On an outside thread, yes you can use a non-radiussed threading tool, and only radius the crest. It will certainly fit the nut. I guess most home shop people do their threads like this, at least for threads that do not require to be particularly structurally sound.

The problem is that the sharp thread valleys, that is where fatigue cracks will start. Think of a thread on the shaft of a petrol motor subjected to vibrations. Or think of a bolt subjected to both vibration and high temperatures. Or... a bolt in aicraft subjected to vibration, cold and hot and bolt failure would be tragic... In all those cases you better stick to the published thread specifications and tolerances.

You can achieve this by using a threading tool with the proper tip radius. But you will need to have several tools with differnt tip radiusses handy. Or a set of indexable threading tools. Or a set of thread chasers. All adds up to cost - fine if you earn a living with it - but maybe not acceptable if its just your hobby. In a humble home shop, you can instead choose to use one threading tool with a very large tip radius, and at the end pass over the thread with a (reasonably good quality) die that will cut both the thread valley radius and the crest radius at the proper tolerance for you.

Originally Posted by cba_melbourne

On an outside thread, yes you can use a non-radiussed threading tool, and only radius the crest. It will certainly fit the nut.

What? How are you going to radius the crest with a single point tool?

Originally Posted by cba_melbourne

The problem is that the sharp thread valleys, that is where fatigue cracks will start. Think of a thread on the shaft of a petrol motor subjected to vibrations. Or think of a bolt subjected to both vibration and high temperatures. Or... a bolt in aicraft subjected to vibration, cold and hot and bolt failure would be tragic..

Which it exactly why BSW is a better thread form and why there is a metric MJ profile.

Originally Posted by cba_melbourne

In all those cases you better stick to the published thread specifications and tolerances.

Again, if you are that worried about fatigue, don't be using cut threads.

Originally Posted by cba_melbourne

You can achieve this by using a threading tool with the proper tip radius.

As I understand it the "proper tip radius" for ISO and UNC thread forms falls into a pretty wide area. From almost sharp corners to something more BSW like. Maybe all the tip manufactures use the same numbers?



Stuart

>What? How are you going to radius the crest with a single point tool?

With a fine flat file of course. Do a google search for "lathe file". Some folks use emery cloth backed by a flat file.




> Which it exactly why BSW is a better thread form and why there is a metric MJ profile.

BSW is not used for much anymore nowdays, except for water pipes, Meccano toy screws, and brass light fittings. Not applications that traditionally require much accuracy in threading.




>Again, if you are that worried about fatigue, don't be using cut threads.

Why that? There is nothing wrong with cut threads if done right. Its a matter of what the application demands.




>As I understand it the "proper tip radius" for ISO and UNC thread forms falls into a pretty wide area. From almost sharp corners to something more BSW like. Maybe all the tip manufactures use the same numbers?

The tip radius for metric threads is certainly well defined in the standards. If it was not so, why would the makers of threading tools offer "full form" tools at all? Or why would there be taps to different tolerances? Its all about what the thread is being used for in the end. Up to you if you choose to follow the standard, or you choose to simplify on it. If you are making a part for a steam engine, you need not bother about tip radius. If its a part for a petrol engine, it may be better if you did bother somewhat.