Shoebox compressor tricks mods for big bore /other gun guys
OK as some of you know on here , i have now well over 200 hours on my shoebox compressor , i wanted you guys to get some inside scoop tricks ,mods that i have learned/come up with so far on running this compressor , i have a ton of hours wrenching on this compressor , also talking to Tom K on the phone a lot , I am a part of his R&D testing /running of the shoebox since i have a ton of cylinders ,and shooting big bore airguns using a ton of air , he has been helping out with things/parts to try out, and test,
OK I think the most important thing you can do is elign the piston rods ,to the cylinder bore holes , and reshape the end of the pistons and polish them , VERY CRITICAL MODS !
Start off by taking the pistons ,and cylinders off, take all the parts out of them / orings check valve , then bore sight the alignment on the pistons to the cylinder bore , you can do this by moving the pistons all the way back on the stroke out , then putting the cylinders back into the main block with all the orings and check valves out so you can see all the way through the cylinder , look through the check valve side of the cylinder use a light behind the other side so you can see how the piston rod alignment to the cylinder hole that it goes back in forth in , now if the alignment is off , you can loosen up the billet block and move it a little until the piston rods are lined up/centered with the cylinder holes, then tighten up the block turn the pistons by hand to make sure everything looks straight , then tighten the block back up
OK now a very VERY CRITICAL mod to do to the pistons , you want to make the front edge of the piston rods look like a round nosed flat point bullet ! here is the deal …..the front of the piston from what i have seen so far is cut flush squared on the end …..this part front of the piston goes in and out of the 1st oring , the second oring the piston shaft stays in it the whole time it runs , so if you have a tapered front piston shaped like a round nose bullet it will go in and out of the oring WAY SMOOTHER ! instead of having a sharp edged bashing it’s way in and out causing failure a lot sooner of the critical 1st oring ,
OK let’s mod the piston , i have come up with a very easy way to do this , before you take out the piston use a long caliper to measure how far it is sticking out of the billet block that it is mounted on { very important to measure this -before you remove them, so you can put them back in at the same length }
after you take them out , put the side that was mounted in the aluminum block in a hand held electric drill , now take a flat file, lay it flat on a bench , then take ,and spin the piston rod with the drill at a slight angel and start grinding shaping the end of the piston rod on the file to make the front of it look like a round nose with a small center flat point ,change the angle as you grind to make a nice rounded smooth bullet shape to it .
you can hold the piston with a rag on it while it is spinning to put pressure on it against the file while shaping it.
once you have a decent rounded shape using the file , then use some 400-500 grit sand on that area you just shaped by spinning the rod in the paper in your hand to smooth it out , then switch over to 1000-1500 grit paper now spin the piston rod again this time not only smooth the bullet shaped end out but also smooth the whole piston rod out by spinning the piston and moving the ultra fine sand paper back , and forth polishing the piston rod up real good , this ultra smooth finish with tapered bullet shaped end , with correct piston rod alignment, will make the o’rings last way WAY LONGER ! ! 😉 😆
All Replies
7 hours in 2 months it will be a year or so before you would probably need a rebuild. It’s guys like you that the ShoeBox is perfect for.
Tom
So for us .25 guys (which means minimum air compared to the big bores)
What is the life expectency of the o rings? I have filled my 4500 psi piggy from zeero once and from 3200 once. I have filled two large scuba tanks from 2500 psi to 3100 psi. (not in a row and not more than an hour and a half or so straight. Is it the heat that gets them? I run a fan all the time on the shoebox. I grease every hour without fail. total time on mine maybe 7 hours in 2 months.
Just so it’s clear, we DO hand polish the ends of all the pistons before we assemble them. If you take a look you will see that the radius of the polish extends to the inner part of the oring.
In Dan’s case we sent him some fresh experimental pistons and they didn’t get the polished edge before we sent them. That’s why we had a discussion about rounding the ends.
Now you can bullet shape the end of the pistons but you will see a drop in efficiency. This is because any air gap at the end of the stroke, reduces the compression ratio and hence the efficiency. You want the end of the piston to squeeze out ALL the air it can at the end of the stroke.
FYI
Tom Kaye
Hi Tom , with what i have done to my pisitons , air time fills on 44cf /88cf tanks is still very good , i have not noticed much of a time to charge difference in-between the 2 , of course as you know for myself charging for big bore guns , i am after how long i can make the orings last , for these longer charging sessions that i have to do , to get all that air ,
thanks for all your help on my shoebox Tom
Dan ,
No its not possible.
TK
Would it be possible to redesign the system so that o-ring is on the piston and not the cylinder???
Guys,
Just so it’s clear, we DO hand polish the ends of all the pistons before we assemble them. If you take a look you will see that the radius of the polish extends to the inner part of the oring.
In Dan’s case we sent him some fresh experimental pistons and they didn’t get the polished edge before we sent them. That’s why we had a discussion about rounding the ends.
Now you can bullet shape the end of the pistons but you will see a drop in efficiency. This is because any air gap at the end of the stroke, reduces the compression ratio and hence the efficiency. You want the end of the piston to squeeze out ALL the air it can at the end of the stroke.
FYI
Tom Kaye
Silly question really, 😆 Now this oring chewer has been found, of course the design will change.
And having the piston rods already lined up with the cylinder bore holes would be nice. In a put together properly kind of way… 😉
well it’s not that the piston rods are not lined up new , but it would be a good thing to check when you rebuild the cylinders just to make sure they are correct , once i figured out that the end of the piston goes in and out of the the #1 oring , i started modifying the piston end, and found that the round bullet shape makes the transition to the piston entering the oring way smoother , you can feel the difference when you change the orings in the cylinder , the cylinder goes on a lot easier with the bullet round nosed shape pistons , and polishing the whole piston rod with 1000-1500 grit paper makes the piston less abrasive to the orings.
I have found that when mine stops working most of the time it is the inner oring being shredded like you say.
Regards,
Roachcreek
yep that 1st oring is key , that is why the round nose bullet shaped piston end is important , to cause less damage to the critical sealing oring .
Dan,
I have found that when mine stops working most of the time it is the inner oring being shredded like you say.
Regards,
Roachcreek
As part of the R&D team and having identified this major problem, will the newer shoeboxes come out with this design modification?
Silly question really, 😆 Now this oring chewer has been found, of course the design will change.
And having the piston rods already lined up with the cylinder bore holes would be nice. In a put together properly kind of way… 😉
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OK I think the most important thing you can do is elign the piston rods ,to the cylinder bore holes , and reshape the end of the pistons and polish them , VERY CRITICAL MODS !
Start off by taking the pistons ,and cylinders off, take all the parts out of them / orings check valve , then bore sight the alignment on the pistons to the cylinder bore , you can do this by moving the pistons all the way back on the stroke out , then putting the cylinders back into the main block with all the orings and check valves out so you can see all the way through the cylinder , look through the check valve side of the cylinder use a light behind the other side so you can see how the piston rod alignment to the cylinder hole that it goes back in forth in , now if the alignment is off , you can loosen up the billet block and move it a little until the piston rods are lined up/centered with the cylinder holes, then tighten up the block turn the pistons by hand to make sure everything looks straight , then tighten the block back up
OK now a very VERY CRITICAL mod to do to the pistons , you want to make the front edge of the piston rods look like a round nosed flat point bullet ! here is the deal …..the front of the piston from what i have seen so far is cut flush squared on the end …..this part front of the piston goes in and out of the 1st oring , the second oring the piston shaft stays in it the whole time it runs , so if you have a tapered front piston shaped like a round nose bullet it will go in and out of the oring WAY SMOOTHER ! instead of having a sharp edged bashing it’s way in and out causing failure a lot sooner of the critical 1st oring ,
OK let’s mod the piston , i have come up with a very easy way to do this , before you take out the piston use a long caliper to measure how far it is sticking out of the billet block that it is mounted on { very important to measure this -before you remove them, so you can put them back in at the same length }
after you take them out , put the side that was mounted in the aluminum block in a hand held electric drill , now take a flat file, lay it flat on a bench , then take ,and spin the piston rod with the drill at a slight angel and start grinding shaping the end of the piston rod on the file to make the front of it look like a round nose with a small center flat point ,change the angle as you grind to make a nice rounded smooth bullet shape to it .
you can hold the piston with a rag on it while it is spinning to put pressure on it against the file while shaping it.
once you have a decent rounded shape using the file , then use some 400-500 grit sand on that area you just shaped by spinning the rod in the paper in your hand to smooth it out , then switch over to 1000-1500 grit paper now spin the piston rod again this time not only smooth the bullet shaped end out but also smooth the whole piston rod out by spinning the piston and moving the ultra fine sand paper back , and forth polishing the piston rod up real good , this ultra smooth finish with tapered bullet shaped end , with correct piston rod alignment, will make the o’rings last way WAY LONGER ! ! 😉 😆
Thankfully Mr Kaye is also a member to offer the correct details. Thanks for that!
Just so it’s clear, we DO hand polish the ends of all the pistons before we assemble them. If you take a look you will see that the radius of the polish extends to the inner part of the oring.
In Dan’s case we sent him some fresh experimental pistons and they didn’t get the polished edge before we sent them. That’s why we had a discussion about rounding the ends.
Now you can bullet shape the end of the pistons but you will see a drop in efficiency. This is because any air gap at the end of the stroke, reduces the compression ratio and hence the efficiency. You want the end of the piston to squeeze out ALL the air it can at the end of the stroke.
FYI
Tom Kaye