Wikipedia:Reference desk/Archives/Science/2017 September 22

= September 22 =

open source stereolithography shrinkage compensation
I've been ordering a few 3D printed parts made with stereolithography. As with most additive manufacturing methods, the produced net shape is different from the input design file due to various factors like shrinkage and warping. So far, I've been manually compensating for this in my design files, i.e. if I want a 2mm hole, I must manually key in 2.05mm to compensate for the shrinkage. Doing it manually presents three problems:

1. It's time consuming since it must be done for every feature

2. Manual work contains errors, missing the compensation for 1 feature out of 100 and the whole part is junk

3. The master parts file now deviates from the actual part shape. So before using another manufacturing method every compensation must be manually undone. God help me if I ever had to a 3D printing -> milling -> 3D printing -> milling round trip.

I found a few academic literature about using offline software algorithms to automatically compensate for shrinkage and warping. Are there any open source software out there that implement these algorithms? Mũeller (talk) 01:58, 22 September 2017 (UTC)


 * I have no direct advice but would point out that 300years of experience designing cast iron parts may have produced some relevant methodologies.Greglocock (talk) 06:10, 22 September 2017 (UTC)
 * If you have confirmed that parts are consistently 2.5% undersized, that is a systematic error that should be corrected in the 3D printer setup for everyone, not compensated by distorting your own design files. The issue of non-proportional shrinkage addressed in one of your links is particularly challenging because of stresses arising in the part. Good sources of information about available software can be the equipment suppliers such as formlabs, GPI Prototype, ProtoCAM, Stratasys, etc. Blooteuth (talk) 14:34, 22 September 2017 (UTC)
 * Yes, the shrinkage is non-proportional. It varies depending on the size of the part and the part geometry. Mũeller (talk) 00:04, 23 September 2017 (UTC)

Gas port location to lessen muzzle rise?
Does the placement of the gas port on a gas operated SA weapon affect muzzle rise? Will putting the port either on top or the bottom of the barrel lessen or counteract it? Or is it a tiny benefit to a problem mostly mitigated by putting the stock in line with the receiver? Thanks, L3X1 (distænt write)  02:45, 22 September 2017 (UTC)


 * Which kind of gas operation are you talking about? See Gas-operated reloading. Most of the systems on that page appear to expel the gas after the bullet has left the barrel and the muzzle has risen. --Guy Macon (talk) 05:44, 22 September 2017 (UTC)
 * I didn't have a specific operation in mind, I was just wondering the force of gas being expelled either up or down would be a significant force in comparison with brakes and stock placement. L3X1 (distænt write)  13:30, 22 September 2017 (UTC)
 * See Muzzle brake. 2601:646:8E01:7E0B:EDA1:6DA2:2F4C:8E0A (talk) 07:34, 22 September 2017 (UTC)


 * Muzzle brakes work well, but L3X1 asked about gas ports. --Guy Macon (talk) 08:52, 22 September 2017 (UTC)
 * Some muzzle brakes have gas ports on top, in case you don't know (BTW, the article describes these in a lot of detail!) 2601:646:8E01:7E0B:EDA1:6DA2:2F4C:8E0A (talk) 07:35, 23 September 2017 (UTC)


 * A gas port on a gas operated weapon and what you are calling a gas port on a muzzle brake are two completely different concepts, in case you don't know. The original question asked about a gas port on a gas operated SA weapon, not about a muzzle brake. --Guy Macon (talk) 11:46, 23 September 2017 (UTC)


 * See muzzle brake, also the AK series of assault rifles. Gas operated weapons use powerful cartridges (low powered cartridges tend to use recoil actions) and so there's a lot of energy left in the muzzle blast. The shaping of the muzzle will have far more influence than the gas port. Andy Dingley (talk) 09:15, 22 September 2017 (UTC)


 * Pistol compensation generally has a port cut in the barrel. They are called "ported barrels" and for semi-automatic pistols, there is either a cut in the slide or the ported barrel extends beyond the slide.  This is to reduce muzzle flip.  On an auto-loading rifle, the term "gas port" is used to describe a hole in the barrel that capture a small amount of gas to operate the bolt. A "gas block" is the hardware that captures the gas and either directs it to the bolt or operates a piston.  That gas port does not affect or compensate for recoil or muzzle rise. Rifles generally attach a muzzle brake, flash hider or compensator by threading the barrel and screwing the devices on the end of the barrel.  --DHeyward (talk) 10:29, 23 September 2017 (UTC)


 * The above is 100% correct. And one of the main reasons why the autoloading rifle gas port does not affect or compensate for recoil or muzzle rise is because it happens too late. The muzzle brake has an effect as the bullet leaves the barrel. The port cut into the barrel design works a bit earlier that that. The gas port that is part of the system that moves the bolt doesn't expel any significant amount of gas until later. --Guy Macon (talk) 11:46, 23 September 2017 (UTC)


 * An interesting detail regarding the fact that rifles generally attach a muzzle brake, flash hider or compensator by threading the barrel and screwing the devices on the end of the barrel: if the device is screw-on, the measurement to determine if the barrel is over 16 inches long is performed with it removed. If the device is permanently attached it is considered to be part of the barrel. Pinning and welding over the pin head is the most popular technique for doing this. See [ http://www.thefirearmblog.com/blog/2016/08/22/gunsmith-pin-weld/ ]. --Guy Macon (talk) 19:58, 23 September 2017 (UTC)


 * While true that barrel length in a rifle must be 16" to avoid being an NFA designated "short-barrel rifle by the ATF, much more nebulous definitions of "rifle" make barrel length much less of an issue. The tortured definitions of pistol vs. rifle with the inrroduction and approval of "stabilizing braces."  ATF considers this a pistol, not subject to the 16" barrel or the overall length requirements.  ATF [considers this] to be a short barrelled rifle.  The receiver, barrel, ammo, optics and magazines are identical.  --DHeyward (talk) 04:40, 24 September 2017 (UTC)