GK1 probe 99 cents

[WobblyHand]

Ordered this earlier today, it has "shipped".  Probe was advertised as Artemis Snowpeak (7mm) on AliExpress.  Hope to get it in a couple of weeks.  Only downside, you can only order 1.  Still, 99 cents shipped for a GK1 probe is pretty darned good.  We'll see if it is any good when (or if) it gets delivered.

[TorqueMaster]

I used to see great deals like that until I started buying stuff regularly.  Are you by chance a new AE customer? 

The stuff is often still crazy cheap there, but those new customer deals were a big draw.
Ok, I do see some .99 deals, freeship if I buy 3+ but no search engine I can find, just endless pages of stuff...

[WobblyHand]

I used to see great deals like that until I started buying stuff regularly.  Are you by chance a new AE customer? 

The stuff is often still crazy cheap there, but those new customer deals were a big draw.
Ok, I do see some .99 deals, freeship if I buy 3+ but no search engine I can find, just endless pages of stuff...

Used to buy there often, but not lately.  Mostly because it seemed overpriced.  Just before the end of the year, it was 99 cents and free shipping for six vendors, but only was allowed 1 unit.  I've found some good bargains over the years, things at 10% the prices here.  A couple clunkers, but that's the risk you take.  I don't buy expensive stuff there, that seems dicey, but machine tooling and grinding discs are fair game.

Agree that their search engine is pitiful.  They'd sell a lot more (to me) if their search was better.

[Back_Roads]

I used to see great deals like that until I started buying stuff regularly.  Are you by chance a new AE customer? 

The stuff is often still crazy cheap there, but those new customer deals were a big draw.
Ok, I do see some .99 deals, freeship if I buy 3+ but no search engine I can find, just endless pages of stuff...

Used to buy there often, but not lately.  Mostly because it seemed overpriced.  Just before the end of the year, it was 99 cents and free shipping for six vendors, but only was allowed 1 unit.  I've found some good bargains over the years, things at 10% the prices here.  A couple clunkers, but that's the risk you take.  I don't buy expensive stuff there, that seems dicey, but machine tooling and grinding discs are fair game.

Agree that their search engine is pitiful.  They'd sell a lot more (to me) if their search was better.

I find it fun to hunt their website, sometimes one even harvest a bargain LOL

[WobblyHand]

Saw this strange person jump out of their car, wearing a blue vest which said "Express".  He ran to the house and dropped off something.  It's pretty chilly this morning.  Anyways, it was the GK1 probe.  99 cents and delivered in 8 days. 

The entrance hole is quite large, 3.54mm, which gives a 1.32mm (0.052") wall at the QD end where it necks down.  The narrow hole diameter seems to be 2.5mm.  Estimated wall thickness is 1.725mm.  I didn't remove the o-rings to measure the groove diameter.  This probably will work, but not positive about holding 4500 psi or greater.  Made me a little uneasy.

Looked at a hoop stress.

P = 35 MPa
OD = 6.18mm (6.18e-3m)
ID = 3.54mm (3.54e-3m)
t = (OD-ID)/2 = 1.32mm
Dm (mean diameter) = (OD+ID)/2 = 4.86mm
stress = P * Dm / (2*t)

stress = 35MPa * 4.86 / ( 2 * 1.32 ) = 64.4 MPa
yield strength A36 steel = 250 MPa

"Safety factor" = yield strength/stress = 250/64.4 = 3.88

But this is not a thin wall, it is a thick wall.  Peak stress occurs at the inner radius.  I get a peak tangential stress of 69.2 MPa.  So the safety factor is 250/69.2 = 3.6.
BTW, a lot of the online calculators have sloppy or incorrect equations.  Seems these guys don't count their parentheses, nor check their equations.  Even engineers edge had problems with parentheses.

[WobblyHand]

Materials matter a lot.  Here's the estimated ratio between yield strength of the material and the max stress.  Calculated for 35MPa

A36, Ratio 3.61
A283 low tensile strength, Ratio 2.38
1020 hot rolled, Ratio 2.96
1045 hot rolled, Ratio 4.19
4140 (annealed), Ratio 5.98
1144, Ratio 8.96
304 annealed, Ratio 3.4

So if the probe was made of A283 I wouldn't use it, there's insufficient margin, especially if the part was dropped or mechanically stressed.
If made of 1144, 1045 or 4140 I wouldn't hesitate to use it.

A283 is the worst grade of steel that I could find properties on.  Not sure what the actual material is, but it is not magnetic.  This means it might be 304 stainless.  Annealed 304 has a yield of 235MPa. 

Now I don't run at 35MPa, best I can do is 32MPa on my pump.  So at 32MPa, the ratio for annealed 304 stainless is 3.72.  Dunno, seems ok.  Shouldn't die instantly anyways...

Lot of work for 99 cents!

[Joekrooz]

Wow, .99!  I paid $18 for spare GK1 probe at GoGun.com  Looks to be same as original.

[WobblyHand]

I bought a probe earlier for $17.95.  The holes were bigger than the original that came with the GK1. 

Thought I'd take a chance on this probe at 99 cents.  I'm not comfortable with it.  I don't know the material (although it's likely to be 304 stainless) and I'm surprised at the huge holes compared to the original probe. 

The OEM probe had a 6.45 OD and 2.5 ID, vs Ali's 6.18 OD and 3.54 ID.  The OEM safety factor is 46% greater, for the same material.  Assuming 304, the original had a safety factor of 5.44, whereas the Aliexpress one is 3.72.  The more I think about it, it's a "bargain" that really isn't one.  I will end up making some because I don't quite trust this piece. 

[Mr.P]

Also the OEM fillprobe is made out of some kind of unusually hard metal - unlike any other fill probe on any other gun I have. It's the only one that doesn't show dimples / dents from the ball bearings that serve to retain the foster fitting.