Very low cost Pick and Place kit

[langwadt]

I absolutely agree that you need the blow off to get somewhat decent reliability.

I placed quite a bit of components for prototyping manually, and I don't remember them sticking to the nozzle (well if you dip the nozzle into flux or paste, that's another story). How come this is such a problem with machines?

From what I've read, it isn't a problem. Apparently, when the component is placed, the surface tension of the paste pulls it off the nozzle.

Pumps I found interesting:
https://www.aliexpress.com/item/32863883713.html?spm=a2g0o.productlist.0.0.4d7d73cdfqFFcb&algo_pvid=c5abc8d4-f9e8-4e49-a8fa-f7eb2891df02&algo_expid=c5abc8d4-f9e8-4e49-a8fa-f7eb2891df02-4&btsid=ce5a9812-1180-4322-8446-af36515867df&ws_ab_test=searchweb0_0,searchweb201602_7,searchweb201603_52

https://www.aliexpress.com/item/32857665192.html?spm=a2g0o.productlist.0.0.4d7d73cdfqFFcb&algo_pvid=c5abc8d4-f9e8-4e49-a8fa-f7eb2891df02&algo_expid=c5abc8d4-f9e8-4e49-a8fa-f7eb2891df02-11&btsid=ce5a9812-1180-4322-8446-af36515867df&ws_ab_test=searchweb0_0,searchweb201602_7,searchweb201603_52

Don't know if they are adequate or not.

If your loop has no leaks then surface tension is not enough to pull it. Especially if you use the black suction cup at the tip end.
Its a constant balance between air leaking and vacuum.
If your nozzle leaks (simple needle) or loop in general when you stop the pump pressure is equalized fast and surface tension does the job. -> Need more vacuum
If it doesn't leak when you stop the pump it will need more time for pressure to equalize. -> Less vacuum but you need more component in loop (valve)
I believe having big vacuum is the best because
A) You can PWM it or use valves to limit the airflow
B) You can lift heavy parts by using nozzles with suction cup (high vacuum + low leak)
C) You can have higher jerk without worrying about part shifting or falling
D) You can have a more controlled environment by having a vacuum chamber. Direct pump doesn't push - pull air constantly, its more like sawtooth and chamber acts like a cap.

Making lighter head is very important if you use belts for driving the head because momentum couples directly on motor shaft.
If you use trapezoid lead screw most of the momentum doesn't couple to shaft as a rotational vector (depends on screw pitch, smaller pitch = easier to rotate) so you don't need to care about weight and jerk.
The negative is that you loose speed because pitch increased. The cost increases if you use better motors but I would prefer to buy an accurate slow machine than a fast machine that needs constant observation.

use a three way valve

[mrpackethead]

I absolutely agree that you need the blow off to get somewhat decent reliability.

I placed quite a bit of components for prototyping manually, and I don't remember them sticking to the nozzle (well if you dip the nozzle into flux or paste, that's another story). How come this is such a problem with machines?

Its all about reliablity and speed.   Firstly  If you turn the vacumn off, it takes some time for the pressure to return to atmospheric, before the part will drop off.  Applying a postive pressure, makes this happen considerably faster.    And sometimes parts will stick to a nozzle. It removes the issue. 

[SMTech]

The valves in the head of our Essemtec are made by SMC and if you look up the part number are made specifically for surface mount machines. Not about to pull the cover off right now but from memory they are DIN rail mounted, no fancy milling and have pressure adjustment grommets on them.

I would appreciate it if next time the cover needs to come off you can take a picture of the type number 
Sounds like an obtainable  item 

I'd say they were these https://www.smcusa.com/products/vacuum-products/vacuum-generators/ZA~51838 in their manifold form with sensors & filters. The filters need changing at least annually & all sorts of other grot finds its way up the line between nozzle & filter so they need flushing sometimes too. SMC seems to have a selection of fairly similar devices, some of them might be better/cheaper/newer. Other large pneumatics companies may have something similar...

[Bicurico]

Noob question:

As I understand it, this machine will just pick and place.

So please explain:

1) How do you setup the source of the components? How does the machine know where each resistor, etc. are positioned in the "stock"?
2) The machine then picks the component and places it on the correct position. But how is it then soldered? With just a slight blow of air (for instance from the head moving nearby when placing some other component) a small resistor could be dislocated, I would imagine.

Kind regards,
Vitor