Peristaltic Fine Spray: no mist: no fog coolant pump

[Jasonb]

I've got some Tygon fuel line and it is indeed quite a bit stiffer, more like the old red line fuel tubing if you ever used that in the past.

Maybe in a thinner wall section it would be OK in the pump but initial thoughts are that the stuff I have is going to load the pump up a lot as it does not compress anywhere near as easily.

Will do the paraffin test but from what was on RCFlying it seems my thoughts on the problem were right.

[Dave Otto]

https://kinesis-usa.com/knowledgebase/tygon-soft-wall-tubing-for-peristaltic-pumps

Dave

[Hugh Currin]

Mike:  Thanks, that answers my question. The mixing is at the end of the nozzle. Simple. I like the idea of a constant volume pump for coolant. It would give a lot more control than a needle valve I'm now using.

Dave:  That Microdrop system looks more like a no-fog set up? There the coolant reservoir is pressurized with needle valves to control the air and coolant flow separately. From Microdrop's site I didn't see a coolant pump in the system? But the nozzle looks simpler and a lot easier to make than a valve block for a no-fog mister discussed previously. First here and then here.

It would be "easy" to put a solenoid valve on the air supply and a relay on the coolant pump for CNC control. That does leave a valve for air flow and a knob to control the pump under manual control. Those could be computer controlled but harder and less useful. I've not seen G-codes for "more coolant", just coolant on and coolant off. You could use two setting, one using M7 mist command and one M8 flood. But I think these setting require observation of the cut. I've not seen coolant settings along with a feeds and speeds table.

Thank you all, good discussion.

[Vixen]

As with everything else, there is more than one grade to Tygon tubing. The ones identified by Dave are specialy formulated soft wall tubes meant for Peri-pumps. Most probably a completely different tubing to that stiffer material used for model fuel tubes.

If you stick with the low cost Grothen pump you are limited to 1mm wall thickness tube. ie. 1 x 3, 2 x 4 or 3x5. Only the 1 x 3 mm tube gives suitably low flow rates; 11ml/min max.

My system is filled with a pink 5% emulsion of EP287 cutting fluid and tap water. It seems happy after two or three days inside the silicon tube. The water content evapourates gradually with time.

Mike

[Dave Otto]

Mike:  Thanks, that answers my question. The mixing is at the end of the nozzle. Simple. I like the idea of a constant volume pump for coolant. It would give a lot more control than a needle valve I'm now using.

Dave:  That Microdrop system looks more like a no-fog set up? There the coolant reservoir is pressurized with needle valves to control the air and coolant flow separately. From Microdrop's site I didn't see a coolant pump in the system? But the nozzle looks simpler and a lot easier to make than a valve block for a no-fog mister discussed previously. First here and then here.

It would be "easy" to put a solenoid valve on the air supply and a relay on the coolant pump for CNC control. That does leave a valve for air flow and a knob to control the pump under manual control. Those could be computer controlled but harder and less useful. I've not seen G-codes for "more coolant", just coolant on and coolant off. You could use two setting, one using M7 mist command and one M8 flood. But I think these setting require observation of the cut. I've not seen coolant settings along with a feeds and speeds table.

Thank you all, good discussion.

Hugh, your are correct this is a no fog system and the small lube reservoir is pressurized. With the low volume of fluid and dual delivery I thought that was also Mike's intent.

I have an air solenoid in my CNC control box and it is mapped so M7 turns it on and M9 turns it off. The adjustments are still manual and for what I do is fine. If I just want air for plastics etc. I just shut the lube needle valves off.  There are at least two industrial quality systems that I know of the Trico Microdrop and Acculube, Lots of home grown stuff on the internet probably because these are ridiculously expensive. The Acculube unit has a small pneumatically operated pump which is gravity feed from the small reservoir.

Microdrop's claim is that all the lubricant is consumed in the cut so very little is used, and there is no mess. This is pretty much true, I can go for months or over a year sometimes on one fill of the reservoir, which holds maybe a pint. Both companies have there proprietary lubes and and are also not inexpensive. I started out years ago with Microdrop's vegetable based formula and it gummed everything up any dried to a sticky goo. After I worked my way through that I switched over to their synthetic formula which doesn't have these bad habits.

Dave

[Vixen]

Hi Mike

Your new system works very much the same way as the Microdrop system I use on my mill, that is as far as how the lubricant is delivered to the tip. The Microdrop does use a pressurized container which forces the lube through the line and does use needle valves for air and fluid control. I have never had an issue setting these.

I took a few minutes to sketch up the Microdrop nozzle, I thought you might find it interesting. They are easy to make and would improve the performance of your system.
Attached are a few screen shots of the assembly. The brass hex has had the points turned down and the Loc-Line nozzle has been reamed so the brass tip is nice push fit into the Loc-Line tip. The lube flows up the center and the air comes down the flats. You can see as the air flows down the tip it collects the droplets of fluid and carries them on to your part. 

Dave

Hello Dave,

Yes, I can see how centralising the fluid jet could help. One question, what is the hole diameter of the fluid jet?

Thanks

Mike

[Dave Otto]

Hi Mike

I measure .04" on the ones I have here, they get kind of beat up from hitting the cutter sometimes, so be sure to make some extras.
Attached is a picture of an original with the integral hose barb. The screw in barb fitting is what I came up with to keep from having to drill a .04" hole clear through the part. The barb fittings are threaded #10-32 which is a common pneumatic fitting on this side of the pond.
Also notice that the turning on the hex only goes a short way, this acts as a stop when pushing the brass tip into the Loc-Line nozzle from the rear. What I modeled earlier was from memory because I was a work.

Dave

[Vixen]

Thanks Dave

0.04", lets call it 1.0mm. Thats the same size as the fine brass tube I have at the moment. Maybe, I just need a way to hold the brass tube central. 

Mike

[Dave Otto]

It seems that you could benefit from some restriction of the air stream to speed it up and help clear the chips. I know lots of people do it, but re-cutting chips is hard on cutters and leads to a crappy surface finish. The hole in the Loc-Line nozzle is quite large so the air velocity would not be that great, more like a gentle breeze. 

Dave

[Hugh Currin]

Dave:

I think we want consistent control of droplets, non-atomized, put into a separately controlled air flow. My home brew no-fog system doesn't give good control of fluid flow. It could be missadjustment of tank pressure or some other adjustment. It can also fog up the shop on long runs. It is better than the siphoning Kool Mist unit I used before. I've not used a Microdrop system and it may be much better. Mike's is interesting, using a pump for consistency. I've assumed that's what he's shooting for?

I haven't connected mine to the cnc control yet. It is on the list along with spindle control, limit switches and home switches. I'm working on two new benchtop machines that I need mist systems for. Very interested in Mike's results.

I'm using Kool Mist with water, a hold over from the Kool Mist system. It's pretty clean and can sit for weeks without cruding up the system. But I have no idea if I could get better results with a different fluid. I've convinced myself the Kool Mist isn't too hazardous to my health, and am leery about other fluids. If the system really didn't fog I'd be less worried.

Thanks.

Hugh, your are correct this is a no fog system and the small lube reservoir is pressurized. With the low volume of fluid and dual delivery I thought that was also Mike's intent.

I have an air solenoid in my CNC control box and it is mapped so M7 turns it on and M9 turns it off. The adjustments are still manual and for what I do is fine. If I just want air for plastics etc. I just shut the lube needle valves off.  There are at least two industrial quality systems that I know of the Trico Microdrop and Acculube, Lots of home grown stuff on the internet probably because these are ridiculously expensive. The Acculube unit has a small pneumatically operated pump which is gravity feed from the small reservoir.

Microdrop's claim is that all the lubricant is consumed in the cut so very little is used, and there is no mess. This is pretty much true, I can go for months or over a year sometimes on one fill of the reservoir, which holds maybe a pint. Both companies have there proprietary lubes and and are also not inexpensive. I started out years ago with Microdrop's vegetable based formula and it gummed everything up any dried to a sticky goo. After I worked my way through that I switched over to their synthetic formula which doesn't have these bad habits.

Dave

[Jasonb]

Well I've had a spending spree on e-bay and now it's just a case of waiting for the bits to arrive, I did include some 1mm x 3mm tube but could only find the Tygon F-404-A listed as fuel tube which I assume does not have the plastisizer added so will see about a different liquid if as I suspect the paraffin will swell the tube. (thanks for the chart Dave)

I'm going to try a different mixing method. There will be a "block" on the head of the mill with a 6mm push fit socket for incoming air, a 4mm one for incoming liquid from the pump and a BSP thread to take the smallest size loc-line that I already have. This is similar to the Cold End arrangement. The stop valve and regulator for air flow will be at the front of the machine, pump control not sure yet.

However my loc-line only acts to position the end where I want it, inside I have run a 4mm OD pneumatic PU tube and the outlet end of that has a small length of brass tube pressed in with a 1mm ID. This gives me good velocity for a small air volume and also means if I change to air I won't have so much residual lubricant left in the loc-line

[Vixen]

I did some tests and experiments today using a graduated cylinder and stopwatch. I wanted to measure the lowest reliable flow rate of the peristaltic pump. The PWM knob was turned down to find the lowest pump speed that would run reliable and would always restart. This was found to be 1 drop per second, which equates to 2 ml. per minute. The minimum flow rate did not change with or without the air blast.

I experimented with different supply voltages, from 6 volt to 18 volt to see if this could improve the slow speed running. Although the PWM knob position altered, the lowest reliable flow rate remained unchanged at 2 ml per minute. I guess the same number of watts are required to break out and restart the pump whatever supply voltage is used.

With the air blast applied the spray pattern was not unlike the pattern shown in Sebastian End's you-tube videos. My spray pattern consisted of small non-atomised fluid droplets no mist and definitly no fog. The air blast easily clears the chips from the cutting zone. That appeared to have achieved my first set of objectives.





To test the system while cutting metal, I did an adaptive clearance on a scrap block of 6082 T6 (HE 30) aliminium. Spindle speed 5300 RPM, cutter 7.0 mm dia two flute, 8.5 mm deep Ap (depth of cut) 1.2 D and Ae (width of cut) of 0.1D and a feed rate of 450 mm per minute. This was my most aggressive machining cut todate, it felt like I could have raised the feed rate further without straining the machine or cutter.

Here is the adaptive clearance underway. The shutter speed of my camera to too slow to capture the rooster tail fo chips flying to all corners of the cabinet. As you can see the cutter and work are well supplied with the pink 5% cutting fluid immulsion. There is actully a lot more fluid being delivered than I expected but it clearly is doing it's job. The water content in the coolant quickly evaporates, leaving a slight oily film over the mill and chips. 



My conclusion is the independant peristaltic coolant pump and separate air supply works well, the flow rates can be controlled independantly and there is no mist or oily fog produced. The fluid flow was a little higher than I expected and further work will be required to reduce the flow. I have reached the limits with what PWM motor control can do to reduce the speed the chosen Peristaltic pump. Next I will try to find some silicone tube with a smaller inner diameter than 1.0mm.  It may be possible to find a different motor with a gear head to reduce the output spindle speed. The alternative is a different type of Peristaltic pump, one with a stepper motor perhaps, similar to the one Sebastion End uses, but the cost and complexity of the motor control system escallates tremendously; out of my pocket money league.

Mike

[Jasonb]

After 24hrs marinating the results for the silicon tube are in.

This was basic RC model fuel tubing, the OD started out at 0.195" (4.95mm), the soluble oil at about a 10% mix had a small effect with the tube measuring 0.203" (5.17mm) but the Paraffin (Kero) took it up to a whopping 0.255" (6.5mm) some 30% increase.

So it looks like an alternative will have to be found for machining Aluminium unless I want to change the tube each time I use the pump. I'm not so keen on something that needs to be diluted as although the water may well evaporate away it is putting that moisture into the workshop air and that could well condense out onto any cold shiny metal surfaces.

[Jasonb]

Mike do you have an idea of what sort of revs the pump was doing at the lowest speed you could get it to work at?

[Vixen]

Hard to tell, I stuck a small piece of masking tape on the very end of the motor shaft to be sure it was turning at the lowest pot setting. I would guess a few hundred RPM, which gives 1 drop per second. Cannot find a way to go slower.

I am currently following up on the stepper motor option. Awating the 'slow boat from China' to deliver a new peri pump head (same type as Sebastions) I have the stepper motor working, as slow as you like, using the 4th axis port.

Mike