Making Acetal leadscrew nuts the easy way

[uhmgawa]

So, going all the way back to posts #129 and #131 back in 2011, Paul Diamond describes using a diesel engine "glow plug" inserted into a piece of hollowed lead screw to create a "hot tap" for form tapping.

Personally I don't find the concept of "hot tapping" particularly compelling. It seems more intuitive to approach thread generation from either a cutting or a molding perspective, the combination of both doesn't seem to offer an advantage over Evan's original molding approach.

He described a series of problem from the glow plug overheating, due to no way of controlling power.

The idea doesn't seem to have generated any interest, and I am curious as to why that is. The solution to controlling power seems straightforward enough. Glow Plugs are simple resistive elements. A PWM (Pulse Width Modulation) circuit using a 555 timer to switch a MOSFET at high frequency can be used to control the duty cycle (via a potentiometer).

I don't think you'd need to get that fancy. The glow plug could be powered from 12VAC, phase cut with a triac to accomplish the same affect. This is similar to the approach used in some older welders to effect heat control. But realistically the thermal mass of the rod is such that even cycling on/off through a relay, etc.. should be enough to regulate temperature within acceptable limits.

The glow plug could also be replaced by a custom heating element made with Nichrome (resistive heating element) wire. Another method entirely is to use a halogen lamp as the heating element. The ones with an external 11.5V AC transformer. These lamps are dimmable using an off the shelf light dimmer, allowing you to control power output. Not sure how small their diameters go though.

If I intended to refine the process I'd probably use a cartridge-style heater (available with integral thermocouples; cheap source: Evilbay) and through-drill the molding thread for a snug fit as the cartridge heater is pressed in. A temperature gradient will exist depending on the heating element and (here molding die's) diameter/length during preheat, and then as heat is transferred to the blank during the molding operation.

Heating the molding die as such is indeed an improvement. At a minimum it offers the opportunity to monitor and regulate die temperature such that the process can be optimized and moreover documented and successfully repeated for a given material and die mass/envelope. Venturing beyond that I'd place additional thermal probes (thermistors would probably work just fine located external to the heating element) close to the die molding surface to capture the temperature profile during the operation.

I can see arguments where form tapping the thread leads to more errors than press forming, but the concept of using an internally heated threaded element can be employed for both.

What concerns me is the uneven nature of the hot-tapping proposition. The threads are formed successively with the initial threads dwelling under heat and semi-turbulent material flow for considerably longer than those at the nut exit. Heat is one concern and may be a non-issue if the temperature is regulated, but the possibility of excessive material mixing concerns me from the perspective of inclusion of impurities or even entrapped air.

The original approach heats the material and displaces it uniformly, through as direct an exit path as possible. As such the opportunity for molding defects should be minimal. Pictures earlier in this discussion of the generated threads seem to support this observation.

[Swarfer]

Yeah, it wasn't the process of hot tapping that got my attention, rather resistively heating the leadscrew. A basic PWM circuit is keeping it simple, complex would be adding temperature controlled feedback Though I would rather use small RTDs than thermistors, for a shorter thermal time constant

I have a couple of metres of 40mm Acetal copolymer and oil filled nylon rod here. I will have to give it a try.

[uhmgawa]

Yeah, it wasn't the process of hot tapping that got my attention, rather resistively heating the leadscrew. A basic PWM circuit is keeping it simple, complex would be adding temperature controlled feedback

My thought was if using a 12V glow plug, controlling 10A+/- of 12V may be easiest through a triac situated on the secondary of a vehicle charger's transformer. Or you could use an SCR on the rectified transformer output. Either would result in PWM at a 120/100Hz rate dependingon line frequency. The thermal inertia is likely to yield a slope of second(s) per degree.

Note inexpensive cartridge heaters are available at power outputs of several hundred watts which operate on local line voltage. So you could dispense with the transformer and just use a light dimmer from the hardware store or one discretely borrowed from the dining room wall.

Though I would rather use small RTDs than thermistors, for a shorter thermal time constant

I have a couple of metres of 40mm Acetal copolymer and oil filled nylon rod here. I will have to give it a try.

Size is probably more significant as whatever you could accurately locate at the die/acetal junction would provide the most relevant information. Although retrieving it may be problematic. Please do share your notes. My block of acetal is still enroute.

[sandiapaul]

What happened to post#1? No pics anymore and only part of the original description is there. I just looked at this a month ago or so and it was all there.

[Peter.]

What happened to post#1? No pics anymore and only part of the original description is there. I just looked at this a month ago or so and it was all there.

Looks like the image has been lost on the ixian website.

[aostling]

Evan told me has decided to take down his website ("virtual reality suicide" he calls it), for reasons having to do with the US and Canadian governments, and a distrust of social media like Facebook.

[sandiapaul]

Hmmm OK but if you search the thread title it seems you can find it elsewhere. I wont post it if Evan does not want it thrown about.
But...the method works, I made a good test today!

[flylo]

That's too bad, Great idea & I thought it should have been a sticky.

[Peter.]

Evan told me has decided to take down his website ("virtual reality suicide" he calls it), for reasons having to do with the US and Canadian governments, and a distrust of social media like Facebook.

Well, that's disappointing. No governments are being punished by removing the pictures, only ordinary people who in the future might be looking for guidance.

[Oldguy]

Just did a quick Google search and found the photos and Evans first few post about making Evanuts at http://www.denfordata.com/bb/viewtopic.php?f=50&t=3727

Glenn

[_Paul_]

This is a real shame this is a useful thread and over six years old and still going, I see the bolt circle calculator in Evans sig has also suffered the same fate as the images.

Just found some of Evans pics on Pinterest search for "Acetal Leadscrew".

[Magicniner]

"virtual reality suicide" he calls it

You'd think he would know that was a thoroughly pointless exercise as it's all cached from various points in time -

Waybackmachine web archive, "Virtual Reality Resurrection" I calls it ;-)

https://archive.org/web/

It will be there in all it's various incarnations for as long as the funding for Waybackmachine is maintained

Use the address in Evan's sig as a source for the URL and you have everything that was ever there ;-)

[John Stevenson]

Give him ten minutes to get his right brain talking to his left brain and he'll rewrite the internet.

Job done.

Will we now have to retitle this thread the Daryllnut ?

See posts # 58 and #69

[RB211]

Due to government differences? Has some one fallen for the fake news fear mongering bs? Thats too bad...

[Magicniner]

Give him ten minutes to get his right brain talking to his left brain and he'll rewrite the internet.

Job done.

Good point John.
But will he tell us how or will it beyond us, or too much hassle to explain to mere mortals, or perhaps it'll be classified? ;-)