.22 LDC bore clearance study print files

[subscriber]

Bruce,

What size are the little holes in CAD, and if you probe them with gauge pins or drill bit shanks?

Thanks

[WobblyHand]

Bruce,

What size are the little holes in CAD, and if you probe them with gauge pins or drill bit shanks?

Thanks

In CAD, they are 1.5mm.  Due to elephant foot, the opening is less than #60 or 0.040".  If I turn the drill bit, it goes through, and the rest of the bore gives some minor resistance to turning.  I need to find my pin vise to do much more, as turning such a small bit by hand is just flirting with a broken bit. 

I'm trading off slight elephant foot for good base adhesion.  Losing a print after 6 out of 6.5 inches are printed, vs minor elephant foot, I would select the elephant foot every time.  Or, if I were to remember - to accommodate it in CAD by opening up the first layer or two.  If I were better at this, I'd remember this finesse stuff every time. 

[subscriber]

Thanks, Bruce

If elephant foot bothers you, why not add a 45 degree chamfer in the CAD file, to both the OD and each hole edge?   Make the chamfer slightly larger than the expected contraction in CAD, print and see if that helps.  I am guessing that a 1 mm chamfer will be plenty, and that 0.5 mm might be enough for most hole edges.

Very few engineering parts have a 90 degree corners.  They are chamfered or have a radiused corner for a bunch of good reasons.  If you don't break the corners in CAD, then use a chamfering tool or file after printing.  The latter is probably wise anyway to remove bumps and cob webs anyway.

[WobblyHand]

At the time, I was battling adhesion issues, so adding chamfers was not a good idea, since they would reduce plate surface area.

On metal parts, if I have access, I do try to either chamfer edges or ease the edges, because they are sharp.  Trying out an off the wall idea of mine, I often leave out those features, since they are mostly niceties.  However, a chamfer or relief might be useful around small holes to reduce narrowing.  For this application, I'd think chamfered vents would be cosmetic. 

For me my next step might be to form structures that circulate the air.  A likely location might be inside the radial sections.

[subscriber]

Chamfering the part in CAD is a matter of degree.  What I was proposing would cancel the closing in of holes, without reducing contact area with the platen.

The opening of the last bore that the pellet travels through should be cleared of plastic that closed that hole down during printing, at least to the extent that a square hole edge is restored.   If platen adhesion is a problem, then cleaning the hole edge after printing seems prudent.   Else, a minimalist chamfer that is added to the CAD file could be used.   OD flare and vent hole edge condition are much less important than the primary projectile path.

[WobblyHand]

Agreed with concentrating on the bore chamfer.  As you said, a minor chamfer of 1mm is all that is actually needed, maybe a little more for cosmetics.

[WobblyHand]

Seems this thread went dormant, both here and on AGN.  Are there any conclusions?  My printer bed is not the flattest, despite my best leveling efforts.  Also had some computer changes, and have finally gotten back to getting my FreeCAD and printing setup working again.  Kind of hard changing computing platforms - a lot of stuff changed. 

Has this effort been overtaken by porous moderators?  They seem kind of neat - kind of muffled and muted, at least from the sound files that were offered.

[subscriber]

Bruce,

Based on the number of participants, the conclusion is that bore to projectile to baffle bore radial clearance should not be reduced below 1 mm.  The gain in performance below that is too small to justify the clipping risk.  The latter is almost verbatim what OldSpook concluded.   As I had proposed 1 mm radial clearance as a good ballpark value, the exercise seems to have confirmed my views.

The fact that some of the smaller clearance data was louder than larger clearance data has been attributed to "too little data".  I can live with that; although I see more going on.  My point was that very little is lost by making baffle bore radial clearances larger; within the 0.5 to 1 mm range.  The results of the study supports that contention.


The effectiveness of porous moderator tube lining looks very promising:
https://www.airgunnation.com/threads/porous-moderator-design-test.1302564/

If you saw the video at the link above of the porous moderator outer tube, with and without foil tape wrapping, the reduction in sound with the tape is very significant.  It seems to vindicate my position on shroud and moderator side vents being as effective as pin striping.   As in, nonsense marketing.  I say this because the porous moderator was full of small side vents and it was very loud until that leak path was closed off by means of the tape.  A few small side vents don't do much harm, but they don't do any good either. Those that state the vents need to be used in conjunction with a fibrous stuffing material are really just blocking off air flow on the inside, making my point for me.

[WobblyHand]

Yeah, my bigboy had clipping right at the exit of the LDC, it was supposed to be 7.25mm, but obviously closed in a little.  After drilling out with an L drill to 0.2900" (7.366mm) I didn't see anymore clipping.  It had those forward vents, aka dog whistles.  But it wasn't spectacular in performance either.  It was quieting, but not enough.  The porous model seemed to have lots of places for the air to loose energy, simply by its structure.

Not quite sure how to do the porous slicing for mine, and keep it intact upon firing.  Probably will take a different approach for the model.  Might print it all with a hard shell, simply to avoid having to wrap it up.  Back to the drawing board...

[subscriber]

All I can advise is to ask those doing porous fill how to set it up.  You could add a hard shell later, if they can't be printed at the same time.  As the porous fill is "fill", it seems that having 100% dense regions around that to print at the same time should be easy.

I think the porous material is not just able to accept air and slow it down, the surface makes a very poor sound reflector.  I have tried designing various porous wall structures, but the part files become massive.  Using the slicer to define those porous areas is much more data efficient.  That is out of my league, as I design stuff for others to print.  My direct printing experience is negligible by comparison.

[WobblyHand]

Think I figured it out.  It's done in the slicer. 

Set the perimeters = 0.  Use gyroid for the fill.  This makes everything gyroid infill (practically speaking).  I need to put in a bigger nozzle, but I will try this out with the existing 0.4mm and use 0.3mm draft mode.  I'm going to try 70% infill.  Hope the thing doesn't blow up on me.  I'll try it on the 2240 first, should be safer.

Same design as before, just porous.  Then I'll wrap it.  I'll figure out a shell later.  Don't think it will be very hard to add the shell. 

[WobblyHand]

Seems there's a bug in the latest firmware for my printer.  After only 30 minutes I got a thermal anomaly alarm.  I remembered that I had gotten a couple before, but they all were after a firmware update.  This alarm paused the print.  There also was excess material on the print.  Resuming the print resulted in a second pause, so I cancelled the print. I found a note on Reddit about excessive extruder current causing this problem.  I edited the gcode to reduce the current by 5%, but it was late at that point.  I'll give it a try later today.  Draft mode current was something like 538 mA originally.

This printer seems to require more attention than I'd like to run well.  I don't want the printer to be the hobby, I want the printed parts to assist my hobbies.

[subscriber]

Bruce,

What printer are you using?

[WobblyHand]

I have a Prusa i3 MK3S+.  I bought it because I didn't want to fiddle with stuff and wanted to just print.  Turns out to be one of the worst designs in terms of ergonomics.  Never seen a piece of kit that is so difficult to assemble, service or repair.  Everything is in the way of something else.  Kind of have to be a contortionist to work on it.  Have to stop ranting about it, or I'll get worked up over it .

Think the thermistor in the hot end has a problem.  The wire was pinched somehow.  But the printer passes all the static tests fine.  Printer self test is fine, the Thermal management cal worked ok, PID calibrated ok.  The thermistor is within reason, resistance wise.  Dynamically, the printer claims a thermal anomaly and quits within a few minutes of a print.  Right now, the printer is dead in the water.  Pretty frustrating.

I ordered a new thermistor, but honestly, I'm not sure this will fix it.  If it doesn't, I'm going to dump it, or shoot it, because it has been an aggravating thorn in my side.  (I'll probably put it aside for a while, and ponder if I should buy a Bambu Labs unit.)

[subscriber]

People that have the Bambu  seem to like them.

[WobblyHand]

The Bambu Labs printers certainly seem quite capable.  Not quite ready to jump ship, but getting awfully close. 

The Prusa hasn't been that easy, it's ergonomics are quite bad, especially for assembly and service.  I'm astonished about it really.  Every time I try to do something, either visibility or access is blocked.  Removing a nozzle is a lot more difficult than it should be, since you can't immobilize the hot end, because you just can't get a wrench on it, because &^^& is in the way.  Not well thought out, in my opinion.

[Back_Roads]

 It sounds like it was made by Ford Motor Company

[WobblyHand]

It sounds like it was made by Ford Motor Company

Actually, one could add most car manufacturers today.  They are designed for minimal assembly cost, rather than ease of service.  When you have to remove the front clip to replace a headlight methinks they've gone too far.  Headlight replacement used to be trivial, not any more!  Believe I heard that's what was needed to be done in an Audi.  I wouldn't know, I can't afford one, nor would I want a car made that way.

[TorqueMaster]

It sounds like it was made by Ford Motor Company

Actually, one could add most car manufacturers today.  They are designed for minimal assembly cost, rather than ease of service.  When you have to remove the front clip to replace a headlight methinks they've gone too far.  Headlight replacement used to be trivial, not any more!  Believe I heard that's what was needed to be done in an Audi.  I wouldn't know, I can't afford one, nor would I want a car made that way.

I could somewhat understand if it was a a "forever" LED headlamp assembly, but no, you are probably correct.  I noticed a buddies 20xx Maxima had dim headlights and offered to install fresh bulbs...until I read about the process -- removing the front fascia/bumper or taking a wheel/fender liner off were the "easy" options.  Not a 2 minute driveway job.  Call me when one burns out!