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Old 10-21-2011, 10:48 AM   #21 (permalink)
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It is called "single point accuracy" it doesn't mean that it's 0.025mm off all the time.
It means if you only take one single point that doesn't relate to anything else in 3D space, it can only guarantee that accuracy.
In normal use you take hundreds or thousands of points that all relate to eachother for positioning in 3d space, so the accuracy of a 3D model made would be more like 0.001mm.
I mostly use the probing arm to get radiuses and angles and position of holes right . Thickness and height are easier taken with a height gauge or a caliper.

It saves me a little time if you do it yourself, I just thought I should offer my help.
Post the plan/pattern when you are done.
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Old 10-23-2011, 12:25 PM   #22 (permalink)
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I made a CAD model of the linkarm and indexfinger.
I have them in Autodesk 2012 .ipt format right now, but can export to a handfull of other formats.
It's dinner time now, but sometime later tonight I'll upload a photo with all needed and some not needed dimensions.
This is a fairly non complex part so a picture blueprint is sufficient for understanding how it looks like.

Here you go: (I uploaded zipped versions of the iges files to the same gallery, but I have no idea where they actually ended up after upload.)
All dimensions are in mm (25,4mm = 1"). (Yells with the ignorant defiant voice: Who uses inches nowdays anyway?)

Link arm:


Index Finger:
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Last edited by Ghostpilot; 11-06-2013 at 05:51 PM. Reason: Bork bork bork. English is my second language
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Old 10-23-2011, 05:44 PM   #23 (permalink)
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It's hard to stop when you sit down to make CAD models.
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Old 10-23-2011, 06:07 PM   #24 (permalink)
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This is NICE buddy!

Let me see how can I build these with these plans;
however, let me know if you need some of these parts; that would be a pleasure to send em to you as you made the effort to share the plans
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Old 10-23-2011, 08:01 PM   #25 (permalink)
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Titansteam: Thank you for the offer. For these particular parts, I made the plans by measuring my existing parts. So I am not in need of any of these right now. However, I do have a handfull of plans for things that hasn't seen the light of day yet, that I will share when they are done (the plans that is), that would be fun to have made and see if they work as intended.

I saw someone trying to convert a Crossman 357 pellet gun to a cal .68 3357. It didn't go too well is seemed. But I want to have a go at it as well. That involves making plans for a new front with or without a built in barrel and a drum. I thought I could make a new front that accept a barrel threading of my choice and maybe add a springloaded tube under the barrel. My idea is to not cram 6 -68 paintballs in the cylinder. Maybe four and add a springloaded tube under the barrel.
Before all that can happen I need to order three or four new parts from a Crossman dealer, as the springy plastic thingy in my 357 was broken off, and it can nor revolve the drum without it.

Just pm me if you want me to send you the models for the parts in the pictures above. I have them in iges format but can export to just about any format you may need.
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Old 10-23-2011, 08:37 PM   #26 (permalink)
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Quote:
Originally Posted by Ghostpilot View Post
Titansteam: Thank you for the offer. For these particular parts, I made the plans by measuring my existing parts. So I am not in need of any of these right now. However, I do have a handfull of plans for things that hasn't seen the light of day yet, that I will share when they are done (the plans that is), that would be fun to have made and see if they work as intended.

I saw someone trying to convert a Crossman 357 pellet gun to a cal .68 3357. It didn't go too well is seemed. But I want to have a go at it as well. That involves making plans for a new front with or without a built in barrel and a drum. I thought I could make a new front that accept a barrel threading of my choice and maybe add a springloaded tube under the barrel. My idea is to not cram 6 -68 paintballs in the cylinder. Maybe four and add a springloaded tube under the barrel.
Before all that can happen I need to order three or four new parts from a Crossman dealer, as the springy plastic thingy in my 357 was broken off, and it can nor revove the drum without it.

Just pm me if you want me to send you the models for the parts in the pictures above. I have them in iges format but can export to just about any format you may need.
That may be an interesting project, especially for the threated front with springfeed ability, regarding to the final cylinder diameter, but there are a few little problems that happens not so easy to fix;

First, cylinder indexing.

If the standard indexing lever/finger works well for the 10 rd .177 cylinder as for the 6 rd .50, will it have enough clearance/force to move a 4rd cylinder, with the effort of the balls in the springfeed pushed toward the cylinders?
That's not the most problematic thing since it is very hypothetic at the moment.

But second, valve limitation;

The 3357 is an old platform with a primitive valve system; it works well as it opens and closes right, but the transfer sections are very tight, and overall the valve body is very small with a little internal volume!

Well, if compaired to a stock sheridan valve it's almost the same, but to counter these parameters you must set a longer dwell, by reducing valve spring, and increasing hammer weight an spring

But here we can't easily play with hammer weight, as they are hardly modifiables, nor the spring, which is specific and you don't have so much place to tare it (even so; if cocking becomes too hard it won't be fun to play with__)
So you get back with one single setting parameter; valve spring.

Then you will have to find the right spring setting not too far from the valve sweet spot because I know that's not letting much space for settings; as you only have one setting factor you will only get one sweetspot, where the valve will be at it's optimal performance.

And if here it won't give the right amout of gaz to eject the ball at even 260fps, it's done!

And I think it will be a huge bit more than in the .50 case. And that's unregarding gaz waste in gaps, that could even be filled and optimized with this newer version.

The best way to do would be certainly studying this valves optimal performances, as I don't see much ameliorations to do on, and then determine if it could be doable to make it shoot .68 caliber paintballs.

That's my point of view :/


And PM inbound buddy
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Old 10-23-2011, 09:44 PM   #27 (permalink)
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That's some neat CAD stuff, but I'm confused as to the necessity of making all those parts. The index finger and barrel latch are currently available parts from Crosman. The only one that's not available is that old style link arm, which will require a pin and washer for where it attaches to the bottom of the hammer. The only advantage of the old style link arm, is the ability to shoot "western style", which I doubt would be something that anyone would want to constantly do, as it's hard to get the hammer back fully each time, plus the valve does not recover very fast, so each successive shot drops off. I've found this out, even with a new valve assembly, shooting rapid double action.

I was thinking about a way to increase the hammer weight, by drilling some holes in the top part and pouring in lead.
A hammer that's heavier at the top shouldn't make it any harder to cock, as you are either pulling it back with your thumb, or using the trigger in single action, and that is just the pressure of the trigger spring and hammer spring.

Another part I have been looking at is the way the hammer strikes the valve. There is an arm that is moved up by the back of the trigger and it stops in front of the valve stem, the hammer strikes this arm which in turn strikes the valve stem. I was looking at some way to have the hammer strike the valve stem directly, to compress it in farther, thus getting more gas through (would need a longer stem, to take up the space of the possibly missing arm, and possibly an extension on the front striking surface of the hammer).
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Last edited by acrewofone; 10-23-2011 at 10:11 PM.
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Old 10-24-2011, 02:28 AM   #28 (permalink)
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I will look into possible space issues if the need arises to redesign the valve to make it bigger. As you said, it is a simple design. Limited space is a problem.
BUT... (a really big one too) a cylinder of a 3357 is larger and longer. What if you could increase the valve size forward, thuss claiming space that normally is occupied by the back portion of the cylinder.
It may be impossible, since I do not hold the 357 in my hand for size reference right now, but it is a thought.
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Old 10-24-2011, 07:01 AM   #29 (permalink)
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Ok I will look at the space in the frame where we could possibly increase the size of the valve.
I though about the lead inserts; it was used in old trains wheels, where lead was cast in a slot on the perimeter, to increase the inertia without adding too much weight,
but in this case you will gain a few grams...We need more energy to hit the valve!
remember the simplified energy formula; E=1/2 m.vē
That means by increasing the weight you will only affect half of what you would by increasing the speed, were it would affect the energy exponentially!
and removing the steel "safety?" rod to earn some hammer travel to let him gain more speed would be a nice beginning

And @Ghostpilot, 357s are not so expensive in Europe? I get mine for 60€, french website but you could find a better offer where you are
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Old 10-24-2011, 08:16 AM   #30 (permalink)
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I bought the one I have off the swedish equivalent to Ebay for a mere 150SEK. Brand new they run for maybe 1000SEK.
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