The pistons are simply steel rods, and if memory serves me correctly they are 1/8" and 3/16" diameters. As they move in and out of the cylinders they are simply displacing the air within.
As in a plunger; with the seal(s) on the outboard end of the cylinder, bearing on the OD of the plunger, correct?
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...
Thanks. So they are itty bitty little things. Hmm, on the 1/8" sounds like gun drill territory. Truly a deep skinny hole.
QuoteAs in a plunger; with the seal(s) on the outboard end of the cylinder, bearing on the OD of the plunger, correct?Yes QuoteIf 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...Exactly
Quote from: WobblyHand on September 28, 2022, 03:11:22 PMThanks. So they are itty bitty little things. Hmm, on the 1/8" sounds like gun drill territory. Truly a deep skinny hole.you can buy precision ground rods that size in stainless steel on amazon for cheap
Quote from: Brett W. on September 28, 2022, 04:55:04 PMQuoteAs in a plunger; with the seal(s) on the outboard end of the cylinder, bearing on the OD of the plunger, correct?Yes QuoteIf 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...ExactlyThanks-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)...Jesse
Quote from: JuryRigger on September 28, 2022, 06:12:43 PMQuote from: Brett W. on September 28, 2022, 04:55:04 PMQuoteAs in a plunger; with the seal(s) on the outboard end of the cylinder, bearing on the OD of the plunger, correct?Yes QuoteIf 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...ExactlyThanks-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)...JesseLet 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?
This has a little info. If I can get it to post.
another
Quote from: WobblyHand on September 28, 2022, 10:34:30 PMQuote from: JuryRigger on September 28, 2022, 06:12:43 PMQuote from: Brett W. on September 28, 2022, 04:55:04 PMQuoteAs in a plunger; with the seal(s) on the outboard end of the cylinder, bearing on the OD of the plunger, correct?Yes QuoteIf 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...ExactlyThanks-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)...JesseLet 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?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,JesseEdited 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...