Author Topic: NEW picts added - Project conclusion (Read 49809 times))

lloyd-ss · « **Reply #80 on:** June 17, 2012, 10:22:02 AM »

It's really making sense now. The pawls either bypass, or catch, depending the direction of motion, so that is how you get the cocking one piston at a time working. Slick!
I know what you mean, it's hard to keep away from a project like that unless you just hide it away somewhere.
Lloyd

Scotchmo · « **Reply #81 on:** June 18, 2012, 03:28:02 AM »

That is an ingenious mechanism! It must have come to you in a dream.

QVTom · « **Reply #82 on:** June 18, 2012, 03:26:16 PM »

Quote

That is an ingenious mechanism! It must have come to you in a dream.

Thanks, The best part is I think it is actually going to work! I spent a lot of time sketching different schemes in various positions of travel and scratching my head a lot. Most of the discarded ideas use a scissors type linkage to cock both pistons conventionally on the back stroke. I think some of those would have worked out well but I was concerned that the cocking effort would be too much due the the high spring force that is required to get the FPE in to the system with the relatively short strokes of the design.

Then I got the idea, it was not in a dream, but an undisclosed location where there is generally ample time to run ideas around in my head

Tom

lloyd-ss · « **Reply #83 on:** June 20, 2012, 07:21:25 PM »

Funny how those inspirations come sometimes!

Arkmaker · « **Reply #84 on:** June 21, 2012, 10:27:05 AM »

Tom,

I just finished this thread and after 40 years machining, I can honestly say I am impressed, very impressed! I have worked with some extremely talented toolmakers over the years, but your their "Daddy".

Seriously, thanks for sharing this project. I don't know springers from a hole in the wall, but I sure know genius when I spot it!!! Looking forward to the finished carbine and testing. You're getting close now....

Rich

QVTom · « **Reply #85 on:** June 21, 2012, 12:24:56 PM »

Quote

but your their "Daddy".

Thanks Rich, your comment gave me a chuckle first thing this morning and that's always a good thing.

Tom

Arkmaker · « **Reply #86 on:** June 22, 2012, 09:03:51 AM »

Glad to start your day off right! Can't wait to see what's coming next.
Rich

QVTom · « **Reply #87 on:** June 30, 2012, 09:32:34 PM »

This is the piston concept. Caution, no actual pictures of parts yet

Front cap - Made from delrin or delrin AF, it protects the seal from extruding into the transfer port. I plan to leave 0.005" clearance with the compression tube wall.

Seal - Turned from PTFE and has a integral o-ring which serves to center the piston head in the bore. I don't know if it is a good idea but it is basically free to add when making the seal. Only testing will tell. May eventually turn into a simple o-ring seal.

Piston - 7068 AL with Tufram 4L coating. Similar to typeIII anodize but harder, more wear resistant, PTFE impregnated and RC60-65 in hardness. Referred to as a synergistic coating because of the way it bonds into the base metal and supposedly won't chip or peel. I have a customer who uses it frequently so I can toss my parts into their lot

Locating Rings - Idea taken from the Scothmo Express, They will be either PTFE o-rings or turned Delrin AF. I plan to test both to see there is any measurable performance difference. Also will try with one and two rings to see if there is a drag penalty.

Roll pins - Because locating rings will need to pass over the cocking slots I'd prefer that they don't rotate and possible tear themselves up.

Screw - Holds the whole mess to the gas spring.

Well it seems that I have made some work for myself

rsterne · « **Reply #88 on:** July 01, 2012, 03:49:04 PM »

Nice design.... seems a bit complex, but I'm sure it will work great....

Bob

lloyd-ss · « **Reply #89 on:** July 02, 2012, 07:08:59 PM »

Tom,
Yup, plenty of activity going on there! Let us know how the machining of the ptfe goes. That is one that will take all the tricks. An integral o-ring? Like an expander? I am sure you already have it in the design, but you might need an o-ring somewhere around the screw threads to stop any blowby.
I am not familiar with either that aluminum or coating. Will have to look it up.
Good stuff!
Lloyd

QVTom · « **Reply #90 on:** July 03, 2012, 02:20:41 PM »

Lloyd,

I hadn't give much thought about the screw other than the 90deg. taper of the flat head would adequately seal against the Delrin. I could put an o-ring in there. somewhere.

The o-ring built into the seal is really more of a locator to prevent the piston from cocking in the bore. It will sized to just barely touch the chamber walls with no compression or squish. It is visible in the picture if you look closely. A square profile may be better for drag, more like a piston ring. I'm clueless when it come to one shape another, round has less contact area but may tend to roll and bind where the square has more contact but may be more stable.

Tom

lloyd-ss · « **Reply #91 on:** July 03, 2012, 11:55:23 PM »

Tom,
OK, makes more sense now. So this is a PTFE lip seal with an o-ring "shaped" integral heel to keep it all centered, with uniform force around the circumference of the lip seal. I have a feeling you might have to machine the "expansion groove" in the seal out to a dimension to accept an o-ring down inside it that will serve to apply expansion pressure on the O.D. of the lip seal. Otherwise, the seal may not have enough time to energize and expand to form an air-tight seal during that short power stroke. The o-ring expander will keep the PTFE lip seal always at the ready. Google PTFE Lip Seal Design, and then click on the Parker design guide. The Parker design guide has a nice decision tree but many of the differences in the design are very subtle and very difficult to achieve without tools of the right geometry. Problem is, I don't even know that that geometry is.
Material is important too. I have found the graphite filled PTFE to wear pretty well. Plain PTFE will work fine for a while and then literally loose its edge. I will say though, that once you hit the right combination of lip design and expander and fit to the bore, it will work very well.

For the o-ring around the flat head screw, machine a .050 deep counter-bore inside the head of the aluminum piston, that is .125 larger in dia than the actual diameter of the threads of the flat head screw. Then use an 0xx series of o-ring to fill the counter-bore and seal any leakage around the flat head screw. The o-ring cross section is .070 dia, and .020 compression is adequate to seal the screw. The leakage may be inconsequential in your dynamic and instantaneous application. I have used this method to seal normally-static applications, but the dynamic should work similarly.
Lloyd-ss

havighurst · « **Reply #92 on:** August 12, 2012, 01:13:37 PM »

Absolutely amazing!!!!

QVTom · « **Reply #93 on:** August 21, 2012, 02:29:17 AM »

I been a little distracted due to my new PCP and some travel but my heart is still with the spring piston gun

I'm down in the shop working on the pistons, I'll have some new pictures for you all soon

Tom

lloyd-ss · « **Reply #94 on:** August 21, 2012, 09:29:06 PM »

That's the spirit Tom !!

Like the Sirene's call, it keeps beckoning you back.

Lloyd-ss

sghr220 · « **Reply #95 on:** August 22, 2012, 10:08:34 PM »

Quote from: QVTom on August 21, 2012, 02:29:17 AM

I been a little distracted due to my new PCP and some travel but my heart is still with the spring piston gun I'm down in the shop working on the pistons, I'll have some new pictures for you all soon

Tom

Are we there yet?.......................Are we there yet?

great project and excellent craftsmanship...also congratulations on the new PCP.

Motorhead · « **Reply #96 on:** November 10, 2012, 02:51:49 AM »

Just found this thread ... Indeed quite the project.
Simple awesome tool and die maker skills at work on this one !!

Progress seems to have stalled ? Last Post August 21st

Bryan Heimann · « **Reply #97 on:** November 10, 2012, 09:45:32 AM »

I wonder if Walther got the idea for the synthetic "piston rings" from you. I've never seen them in an air rifle before I saw them in your design. I hope that you finish her soon!

Supaflee · « **Reply #98 on:** November 10, 2012, 10:47:18 PM »

QVtom , Ive been watching with keen interest , your development , particularly of the pistons with guide rings.
I want to "shoot from the hip " a bit here and suggest to you that the drag induced by the inclusion of the guide rings is going to offset the benefit of them being there at all , and this will be detrimental to the overall function efficiency of this apparatus.
On the opposite end of the piston you have a delrin ring securing the seal and being .0025" clear of the bore's diameter , which I believe is excellent.
Can I suggest that instead of "circumferential guide rings ", machine 3 small flats into the OD of the piston , 120 degrees apart around it's circumference , and insert 3 small pieces , " buttons ", of wear resistant material into the flats to provide a linea and axial guide with near zero drag.
Friction is the going to be the killer of your design efficiency , and for this reason I feel by making a change to the guides , friction will be hugely reduced ...... very simply .
Im keen to hear your comments regarding my suggestion , Regards supaflee

Pellethuntr · « **Reply #99 on:** December 05, 2012, 11:56:56 AM »

This is a fantastic thread.. Machining at it's best

I will be following and learning as this beauty comes to life

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NEW picts added - Project conclusion

Author Topic: NEW picts added - Project conclusion (Read 49809 times))

havighurst

sghr220