Wow, very interesting results. You are collecting enough data for your own book
Quote from: MichaelM on May 08, 2012, 11:22:32 PMinstead of running the threads under power on the lathe you can make you a removable crank that attaches to the rear of the headstock so that when you want to thread you can just attach the crank handle set your compound and select the right gears for your thread.... then you just set your halfnut andstart cranking when you get to the end of your thread you back the compound off a tad reverse crank the handle till your carriadge is back to the beginning run the coupound back in and start cranking again...... basicaly everything you would do under power but your doing it manual and you NEVER disengage your half nuts so you never loose your index with the thread your cutting..... and no need for the threading dial..super simple to make a crank too... just get you some scrap roundstock (delrin alu steel doesnt matter) drill you a hole the length of it, then turn it to just under the size of your headstock bore, then cut the pipe at a angle in the middle.. Get you another peice of scrap round square whatever you got make you a crank arm and handle then take a long bolt and bolt the whole thing together with the tube angles mated together... slide the whole thing into the bore of the headstck tighten the long bolt down and the angled ends try to slide past each other and grip the inside of the bore(Kinda like an old gooseneck on a bike would stay down into the forks) .... you now have a removable crankkinda like this except they have a collet shown attached at awellhttp://homepage.mac.com/bhagenbuch/machine/pages/spindlecrank.htmljust remember to REMOVE the crank before ou power back up!!!!!Michael M,I tried it last night for the same application as scothmo. Worked like a dream!!!No more sweating about crashes or ruined parts.The extra nuts on the right are just spacers for the long carriage bolt I had in the bolt-box.
instead of running the threads under power on the lathe you can make you a removable crank that attaches to the rear of the headstock so that when you want to thread you can just attach the crank handle set your compound and select the right gears for your thread.... then you just set your halfnut andstart cranking when you get to the end of your thread you back the compound off a tad reverse crank the handle till your carriadge is back to the beginning run the coupound back in and start cranking again...... basicaly everything you would do under power but your doing it manual and you NEVER disengage your half nuts so you never loose your index with the thread your cutting..... and no need for the threading dial..super simple to make a crank too... just get you some scrap roundstock (delrin alu steel doesnt matter) drill you a hole the length of it, then turn it to just under the size of your headstock bore, then cut the pipe at a angle in the middle.. Get you another peice of scrap round square whatever you got make you a crank arm and handle then take a long bolt and bolt the whole thing together with the tube angles mated together... slide the whole thing into the bore of the headstck tighten the long bolt down and the angled ends try to slide past each other and grip the inside of the bore(Kinda like an old gooseneck on a bike would stay down into the forks) .... you now have a removable crankkinda like this except they have a collet shown attached at awellhttp://homepage.mac.com/bhagenbuch/machine/pages/spindlecrank.htmljust remember to REMOVE the crank before ou power back up!!!!!
Am I correct that with the heavy piston, at 8.4 FPE, you are virtually right on 4.9 FPE/CI swept volume (28cc = 1.7 CI, right?)....Bob
Scotchmo,All your observations about pellet fit have me wondering about something I have been thinking about for a long time. In a springer, the compression is controlled mainly by the pellet fit, transfer port size, and the weight of the pellet. I wonder if anyone has ever incorporated a little pressure relief poppet that dumps the compressed air into the breech at a consistent pressure? Or what about a mechanical method to open a valve at the end of the piston stroke? I have no idea if either of those thoughts have any merit, but it seems like the resulting gun might be almost like a little pcp. Or maybe not.Lloyd
Congratulations on a fine project and learning experience.... You should be very proud of the results....Bob
It will be VERY interesting to see if your "twice as heavy" piston indeed results in putting the peak of the power curve at, or very close to, 7.9 gr.... I'll be looking forward to those tests....Bob
I made the steel piston yesterday.Mass:1.8 oz. - AL piston5.3 oz - STL pistonThat seems a lot heavier but it is really the total moving mass that counts. The spring contributes a significant amount. The gas spring that I use is about 5.2 oz. total weight. I use half of that number to estimate the moving mass of the spring. Part of it is stationary, and part is moving. So it contributes about 2.6 oz.Total moving mass:4.4 oz. - AL piston and gas spring7.9 oz. - STL piston and gas springThat is about an 80% increase in mass. I was going to go for about 100% but this is close enough for the next round of testing and it did not require any design changes, just material changes. The new steel piston has the groove for the skirt ring. It is a PTFE ring to guide the rear of the piston without needing lube. I had to cut it off of the aluminum piston early on because of a design error. I did end up using some lube in the gun. It still needs it in areas outside the chamber. The compression chamber slides in an aluminum receiver. Steel sliding on aluminum can start galling and then it just snowballs. A little common chassis grease there seemed to smooth things up a lot. Actually lithium based EP grease which is common these days. I also used a little 60% moly on some high load contact areas in the cocking and trigger mechanisms.
Scothmo, The PTFE ring on the skirt, is this something you made or off the shelf? What is the profile? How much clearance are you running on your piston skirt to compression chamber wall? Any thoughts if the PTFE ring reduces drag and probable lifespan? Sorry, lots of questions but It looks like an interesting idea and may help reduce the noise signature of a spring gun. Considering for my project.Tom