Author Topic: NEW picts added - Project conclusion (Read 49733 times))

QVTom · « **Reply #160 on:** June 18, 2013, 07:40:28 PM »

Do two items qualify as a list? Not sure a we actually have a list yet!

OleTomCat · « **Reply #161 on:** June 18, 2013, 07:46:50 PM »

#1: Tom
#2: Al
#3: Larry
#4: ?

There list started....

QVTom · « **Reply #162 on:** July 16, 2013, 02:49:21 AM »

For those of you that are on the list.......

Although the linkage was performing well I noticed some stretch in one of the links so I decided to do some serious analysis. Based on what I leaned I made more design changes and now believe I have a solid system that will last.

This is based on 115 ft/lbs of input power... That's 125 degrees of travel @ 42 lbs. cocking force for both the back and fore stroke.

Anyhoo, time to make some more parts

Hanabata808 · « **Reply #163 on:** July 16, 2013, 04:06:44 AM »

Can't wait to see the revised version!

QVTom · « **Reply #164 on:** July 22, 2013, 07:22:41 PM »

New link made for 4140 steel. They should be good in their annealed state but they can always be heat treated to ~ 85ksi if necessary.

QVTom · « **Reply #165 on:** July 23, 2013, 12:29:25 AM »

More links. 4142 prehard.

The single link on the bottom is the old version that was stretching. New links on the left are much beefier.

Tom

willbird · « **Reply #167 on:** August 29, 2013, 09:52:34 AM »

I did a little lol about the "very low" sfm for the 4142 pre heat treat. In a previous life I made a lot of stuff from aermet 100 which is close to inconel 100, much was done with carbide but a few holes were drilled with HSS tooling, which loafs along at something like 15-18 SFM according to machineries handbook ??

The aermet 100 IS a nice material to do exactly what you describe, make a part that can be hard and strong but NOT require heat treat post machining. The employer at that time used a clamp made from a steel that was heat treated post machining, well one whole batch got ruined in heat treat. Prompting them to try the aermet 100. Looks like it is about 40 rockwell C in the annealed state.

lloyd-ss · « **Reply #168 on:** August 29, 2013, 11:08:48 PM »

Remember those old "Where's the beef?'" commercials? I think it's been found.
There's an old pin-and-link type railroad bridge near where I live that uses links smaller than those.
I'll stop now.

Very nice, Tom. And the FEA must be very helpful in tough situations like this.
Lloyd

QVTom · « **Reply #169 on:** December 31, 2013, 10:06:31 PM »

I haven't posted on my project in a while, mostly due to time constraints not a waning interest. The following are some pictures from the past few months and some conclusions.
\
I'll try to get some finished photos or video up in the next week or so.

Breech design

Gas spring charging contraption

Piston weight adjustment (bad idea)
Before lightening

After lightening

The gun is shooting

and I have been tuning. I've learned a lot during the tuning process, mostly about how little I understood spring guns when I started the design.

Piston weight is probably the most important design element. I started with HS aluminum pistons that were discarded very early on due to the coating that was intended to provide hardness and wear resistance didn't penetrate the 7063 alloy to a sufficient depth. The next set were made from 4130 and they are the ones pictured above. Initial performance with the 4130 pistons was terrible, the gun was producing about 10 fpe. That was about a 1/3 of where I wanted to be so I wrongly decided to lighten the pistons. The lightening of the pistons reduced the velocity by over 100 fps! At least I was on to something, so I incrementally added some brass rings in between the gas spring and piston skirt. Each ring weighed almost an ounce and added about 40 fps. With the brass weights I was able to bring the piston weight from .4 lbs to almost .95lb each. There was no more room for brass, I had reached the max weight with this method. Next I removed the brass weights and poured lead into the pistons, with a little fiddling I got the piston weight matched and was at 1.35 lbs each. Performance was 23 fpe at this point and still far from the design goal. Charging this gas springs from 1600 to 2300 psi increased power to 25 fpe. 2300 psi equates ~ 550 lbs. of force which made the cocking force uncomfortable.

My conclusion is.............. Large piston face/short stroke is unworkable. The large piston face area makes them prone to bounce and it is impossible to make them heavy enough to overcome the bounce. I believe that if I had more space for heavier pistons I could get closer to the design goal. I have an uncompleted longer stroke version with the same bore that could fit heaver pistons but to have 3 lbs. of piston weight seems silly and will make the gun too heavy. Even with the longer stroke, I believe I'd still be on the wrong side of the swept area/piston face curve. The 1.79 dia. piston design ends here. Lesson learned

Now for some good news.......... Completely sans-recoil, if it wasn't for the noise you wouldn't know that it fired! Really, the gun has no motion or vibration period. It's that smooth!

I've considered de-tuning to 18 fpe and using for FT but rejected this idea for a new line of development. As I said, the 1.79 bore is dead.

A sneak look at my new version. A longer stroke and smaller bore. Cocking, sears and breech design will remain the same. One advantage of the longer stroke is that it simplifies the cocking linkage somewhat. Yeah

Tom

rsterne · « **Reply #170 on:** December 31, 2013, 10:16:03 PM »

The king is dead, long live the king.... *RIP*

Sorry to hear that, Tom, it was a gorgeous project from start to finish.... Oh well, you'll enjoy the next one even more, right?.... Happy New Year !!!

Bob

QVTom · « **Reply #171 on:** December 31, 2013, 11:14:19 PM »

Bob, Happy New Year!

If power was the only design goal I'd be very disappointed. Actually, I'm excited about the new design. I see the potential and hopefully can avoid some of the pitfalls. Besides, It's looks good on my wall. LOL!

Tom

Motorhead · « **Reply #172 on:** January 01, 2014, 03:48:24 AM »

Sort of left speechless ... wow, countless hours in brain power and machine time.
We're left feeling that experience is indeed not getting what you wanted .... next

Bryan Heimann · « **Reply #173 on:** January 01, 2014, 10:20:50 PM »

In break barrel guns I have always associated long stroke with increased hold sensitivity. I have always wondered why there are no short stroke magnums with bigger tubes. Now I know! Thanks for the insight! Great work on the gun, I know it hasn't met your expectations in terms of power, but it has blown me away. I can!'to wait to see where you go from here...

Hanabata808 · « **Reply #174 on:** January 02, 2014, 06:05:27 AM »

If you keep the 1600 psi in the gas spring and settle for the 23 fpe, that actually sounds like a really awesome plinker! Especially if you are saying the firing cycle is dead smooth. I'd certainly enjoy plinking with a home-made wonder like that. Perfect for back yard. Even though it's not what you had planned on, I gotta say congratulations on a fine creation! From all the photos you posted thus far, it really looks like an amazing rifle. I'm still on the list right? haha

PetefromTn · « **Reply #175 on:** January 02, 2014, 02:47:41 PM »

Now we're talking... This is some impressive work despite it not meeting your expectations. I am INSANELY JEALOUS of your SOlidworks capabilities. I recently acquired a nice clean Cincinatti Arrow 500 VMC and got it working. Looks like yours is a HAAS perhaps? Nice machines. I ran some briefly in a local shop and they have some nice features. The Whiscombe Air Rifles are works of art and you have created something very similar. I don't honestly see the necessity of it being overly light but that is personal preference. The Whiscombe rifles are not exactly light having shot quite a few over the years. They are however extremely well made and some are precision accurate. What you are doing is very interesting here and I have enjoyed reading the thread. I would love to try something similar. I have built several actions over the years including a decent FT rifle PCP. There seems to be a lot more going on in this mechanism than meets the eye and you have come a long way to getting it working. I think the smaller diameter pistons and slightly longer travel would be the ticket as you have found more like the Whiscombe rifle but you may have something to add here that the other guns do not have. I like your cocking design. That it seems to me to be the most complex part of these rifles. Your transfer port looks quite large too there is a LOT to be gained in sizing that correctly. You may find that the gun shoots to your specs with the slight adjustment of things like that. I LOVE the blow thru bolt you made and that breech is very nice altho the area near the transfer port seems a little thin in cross section. It appears that the port area is a seperate piece that is inserted there no? Lovely work again and I hope to be able to use my VMC for something beautiful like that soon. I am currently covered up with some Custom Woodworking projects that are making me more money than I have been able to get with the Machining despite my best efforts. Personally I like it that way as I would rather do the wood work during the day and then moonlight with some cool airgun stuff anyways. Either way you have some impressive skills man and I look forward to reading and seeing more of your airgun adventure. Please post whenever you are able. Thanks for sharing this impressive work. Peace

Pete

OleTomCat · « **Reply #176 on:** January 02, 2014, 04:11:55 PM »

Tom,

When you start on the new design, please link it back here for ease of locating and continuity of the project....

Al

subscriber · « **Reply #177 on:** April 18, 2018, 04:34:10 AM »

Quote from: QVTom on December 31, 2013, 10:06:31 PM

My conclusion is.............. Large piston face/short stroke is unworkable. The large piston face area makes them prone to bounce and it is impossible to make them heavy enough to overcome the bounce.

Yes, I know it has been years, but, to quell piston bounce, ponder this idea:

Place a reed-valve inside your breech bolt (as used on some two-stroke bike engine intakes) . The valve would snap shut due to the pressure differential, just as the pistons start to bounce back. That would trap the bulk of the air behind the pellet, regardless of what the pistons felt like doing.

2K1TJ · « **Reply #178 on:** April 29, 2018, 12:55:53 AM »

How did I never see this thread! I love to read these type builds!

Did you ever try any other versions of this concept?

Motorhead · « **Reply #179 on:** April 29, 2018, 01:48:41 PM »

Tom went on from here and developed his SLAYER 357 Bull Pup .... AMERICAN AIR ARMS company too

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NEW picts added - Project conclusion

Author Topic: NEW picts added - Project conclusion (Read 49733 times))