All Springer/NP/PCP Air Gun Discussion General > Machine Shop Talk & AG Parts Machining

Anyone know of plans to machine your own HPA compressor?

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--- Quote from: Brett W. on September 28, 2022, 11:42:32 PM ---This has a little info. If I can get it to post.

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Thanks Brett W.  You guys are coming through!  I have seen that gif before.  It's quite informative as it shows the unit in action, which is a lot nicer than a static image.


--- Quote from: Rob M on September 29, 2022, 12:03:51 AM ---another

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Thanks Rob M.  A slightly different take on the design.  Assembly was interesting.  Of course, I have to slow it down, and digest all the info.  Not sure I like his valves at the cylinder ends.  For that matter, I don't know about all those fins.  I'd hate to machine them all like that individually, but doing that would beat scrapping a cylinder with integral fins that you buggered up on the last few fins.  Not clear how those fins really make thermal contact with the cylinder either.  Nonetheless, very interesting.


--- Quote from: JuryRigger on September 29, 2022, 12:17:31 AM ---
--- Quote from: WobblyHand on September 28, 2022, 10:34:30 PM ---
--- Quote from: JuryRigger on September 28, 2022, 06:12:43 PM ---
--- Quote from: Brett W. on September 28, 2022, 04:55:04 PM ---
--- Quote ---As in a plunger; with the seal(s) on the outboard end of the cylinder, bearing on the OD of the plunger, correct?
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--- Quote ---If so, the finish/tolerance of the ID's of the bores would be purely a matter of reducing dead space within the cylinder; as no seal would be bearing against it/them...
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Thanks-maybe the OP should reconsider DOM tube then; as straightness would be critical to eliminate contact between the plungers and the cylinder bore (and would be easier to correct if the material obtained was not straight enough; vs. trying to produce a hole that long/straight by any method)-think you can get it with thick enough walls in those ID's to give enough meat for glands and such, too (at least in steel, which is mostly what I've looked at)...

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Let me ask a question. 

Can one get a precision bore made in DOM?  Like to 0.001" or less?  Doesn't the weld interfere with further processing, like reaming?  How straight is it over say 3 or 4 inches?  Less than 0.001"?  On the other hand, I have no experience using DOM.  Sure I have a roll bar made of it, but I didn't fabricate it.  And, roll bars don't need precision bores ;) 

Just looking at McMaster for DOM tubing, they don't even have a spec on straightness, like they do for other precision products.  Do you know of any sources where DOM is available and there are straightness specs?

Gun drill wander (if done carefully) is on the order of a few thousandths per foot, if I believe the suppliers websites.  How does that compare with what you are thinking.

Another question.  Can one use gun drill in an existing hole?  I don't think that is ordinarily done with gun drills, although I may be totally wrong.  Don't know enough about them.  Wouldn't the drill attempt to follow the hole?

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Can't answer a single question regarding gun drilling, as I have no experience in that department...

Regarding DOM tubing, if it is truly DOM (drawn over mandrel); the weld seam will be invisible (and impossible to find, either by visual inspection, or during machining-if you do you have gotten bad stock, and the mill should hear of it)... In my experience with SAE-J525 1010 hydraulic tubing, the ID is fairly smooth-and generally they are pretty tight on tolerances, IE wall and diameters-again what I've experienced may not be representative of all DOM; and I haven't mic'd all my stock...

Have only one piece quick-to-hand, .5" nominal OD-mics out at .5018-.5019" (mic'd at three points along a 24" length, ten points each searching for min/max out of round)-ID is too small for my telescopic gauges, and I do not know for sure what the spec'd ID was, so can't speak for that on this piece...

As far as straightness goes, all I can say with relative certainty is that it is pretty straight from the mill, can't give you any hard specs, as I've never seen any-I laid the piece I mic'd on my 11" long surface plate, and repeatedly slid it under a test indicator-the most runout I was able to discern, was approximately .00025"...
Again, not representative of all DOM-I have two other pieces that I know of, one 5/8" OD and one 3/4" OD-that are both bent (EG, 1/16" or worse over 24")... Also a bunch of other pieces, that  appear to be perfectly straight (but have not checked)...
I believe that DOM ends up pretty danged straight, as a matter of manufacture-however as it is long and skinny from the mill, it is particularly susceptible to getting bent later on, mostly in slow curves...
One thing to note, DOM tends to be smoother on the inside than the outside; as it is drawn over a mandrel, the OD may have minor ribbing/imperfections...
Hope this is of some help,
Edited to add-while this particular piece of tube is quite fantastically accurate; I would not count on all DOM being that way; though it is possible...
FWIW, this piece was whatever got ordered for a job I used to do, got the piece I have as a leftover drop-the rest of my DOM is Hydrabrite from Plymouth Tube..
Might make a difference, might not-dunno...

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Thanks for your honest answer.  I know practically nothing about gun drills either.  More or less learning as I am going along.  Thanks for the skinny on DOM tubing.  Got to think this all over and come up with a plan, or at least an approach.   At least this will keep me out of trouble for a while...

I was thinking about this thread today for some reason.  Any who, it popped into my head if I was going to build one or had a similar set-up I would feed it with a refrigerator or freezer compressor.  They are capable of higher pressures than your typical shop air compressors.  Of coarse if you feed a tank with it, make sure it is rated for higher pressures as IIRC they are capable of 3-400PSI.  Don't need to build a bomb.

I have a 30gal compressor that the compressor went out on.  I also have a compressor off of an old fridge.  Just haven't gotten around to putting the two of them together.  It has a pressure shut off and also a pressure relief valve. 

They also have a much lower CFM rating than a regular compressor, so it may not supply enough volume.


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