Vacuum hold down box

[Howley]

I just built my box to hold my two light house 220v vacuum motors for my hold down table. When completely sealed I'm measuring 10-11 inches of mercury. It works great!
I leave my 2" purge valve slightly open to give it enough air to cool the bearings, however the exhaust and motors still get very hot!

I know that some people draw air across the compartment that holds the motors.....does this really make a difference?
How much air is really needed? I also read that some even hook up there 1200 CFM vacuums to draw the air.

The only thing that seems to really lower the tempature is to open the purge valve all the way and take the load completely off the motors, then they run really cool, but add a little load and they get very hot. Is this normal?

Please give me your input.

Thank, John

[aschutsky]

John - What kinds of temps are you seeing under load?

[ken_rychlik]

The tops of the motors have fans that draw air in. I put flex hose on those and they bring in outside air from underneath to keep the motors cool. If you didn't do this, I could see the motors melting down.

[Howley]

Not sure what the temps are. I spoke to the gentleman at lighthouse vacuum (very nice and helpful!!) he said that under load the temps could reach 200 degrees. I'm leaving my purge valve open to keep the bearings supplied with enough air and I cut 1/2" wide slots in the top cover to allow heat to escape and cool air to come into the box. I am also thinking about putting a 5" 120 volt high flow fan either on the side or top to force fresh cool air into the box. Hopefully that should do it. :confused:

[curtiss]

I have heard of someone using an indoor / outdoor thermometer sensor to keep an eye on the temperatures.

[jim shula]

I have two of them mounted outside the building to minimize the noise. They were each in a sealed box, and one of them melted down last summer. Since then I took the covers off the boxes.

[aschutsky]

Guys - for those of you using indoor/outdoors to monitor temps, where are you placing the sensors?

[coryatjohn]

I suggest obtaining an inexpensive infrared thermometer. I got a couple around Christmas time for $15 each.

I went with regenerative blowers instead of the Fein setup. There is a lot less noise and the units are designed for continuous operation for years and spin at 3600 RPM. That makes them quite robust. I run two 220v 2HP units in series to get around 8 inches of vacuum. While the Fein's might draw more vacuum, the higher cfm's mean the vacuum holddown pressure remains relatively the same regardless of the cut-throughs.

I paid about $500 each for the regenerative blowers on ebay.

[aschutsky]

John - There are plenty of remote sensor indoor/outdoor thermometers on amazon for 20 bucks each. Most are good up to 150 degrees F. I have an infared setup as well, but it would be nice to have a small 'dashboard' to show real time reading of temp. :cool:

[jTr]

Guys - for those of you using indoor/outdoors to monitor temps, where are you placing the sensors?

I placed mine on the metal housing of motor #1 with self adhesive backing. Typical heat range is 114-120 degrees F.
Yes, I realize motors 2 through 4 are on their own, but at least I have some sense of what's going on inside.

jeff

[aschutsky]

I placed mine on the metal housing of motor #1 with self adhesive backing. Typical heat range is 114-120 degrees F.
Yes, I realize motors 2 through 4 are on their own, but at least I have some sense of what's going on inside.

jeff

Jeff - Perfect, that's exactly what I was thinking. No reason to believe that 2 through 4 would be any different. :)

[aschutsky]

For those using indoor/outdoor thermometers to monitor temperature, how long are you seeing for the 'lag time' between swings in temperature? I was playing with mine last night and it takes a good 2 minutes for the sensor to 'stabilize.'

[jTr]

Andrew,
Like most digital thermometers, there is a lag time - haven't timed mine, but it can take up to 30 minutes in the winter months to warm up from about 63 degrees to normal levels. If I'm running 2 motors and have a pretty tight seal, it can jump from 114 to 120 + pretty quick - a few minutes. Sometimes I can see a drop of a couple degrees within a minute of opening an unused zone, or even flipping on the secondaries.

These motors are reasonably stable, so the general accuracy of this method of monitoring should be enough to confirm either normal or abnormal conditions as long as you're keeping an eye on things.

jeff

[aschutsky]

Andrew,
Like most digital thermometers, there is a lag time - haven't timed mine, but it can take up to 30 minutes in the winter months to warm up from about 63 degrees to normal levels. If I'm running 2 motors and have a pretty tight seal, it can jump from 114 to 120 + pretty quick - a few minutes. Sometimes I can see a drop of a couple degrees within a minute of opening an unused zone, or even flipping on the secondaries.

These motors are reasonably stable, so the general accuracy of this method of monitoring should be enough to confirm either normal or abnormal conditions as long as you're keeping an eye on things.

jeff

Perfect - thanks for your insight. Should be more than enough to get me going. :)

[aschutsky]

Andrew,
Like most digital thermometers, there is a lag time - haven't timed mine, but it can take up to 30 minutes in the winter months to warm up from about 63 degrees to normal levels. If I'm running 2 motors and have a pretty tight seal, it can jump from 114 to 120 + pretty quick - a few minutes. Sometimes I can see a drop of a couple degrees within a minute of opening an unused zone, or even flipping on the secondaries.

These motors are reasonably stable, so the general accuracy of this method of monitoring should be enough to confirm either normal or abnormal conditions as long as you're keeping an eye on things.

jeff


Jeff,

I was toying around running my setup for a few minutes last night and had some interesting observations. With using one zone not sealed off and some additional bleedoff from my valve, I was beginning to approach 130 degrees on the primary motor with the sensor attached to the metal housing. It's possible within a few more minutes the temps would start to drop back down, but I was surprised that it was climbing this high after ~15 minutes of playing around. Is this normal? This was all 4 motors running in my blackbox. I'm amazed at the flow these things provide! I was testing using an approximately 18x24 board on one zone with no masking and the board was still giving me trouble removing it with my 2" bleeder valve completely open, haha! Perhaps my gauge is a bit 'off' from normal standards but as low as 2-3" HG was holding this sized board rather firmly.

[jTr]

I think you'll just need to observe for a few jobs and note what is "normal" for your system. Your heat sensor is likely not placed in the same spot on the motor housing as mine = your normal reading is likely to be a bit different. Just be sure your motors have a separate cooling intake and exhaust pathway, which should be the case if you've built to spec's.

Also - I'm comfortable running only the first pair of motors 85-90% of the time when holding down a full 4x8' sheet of ply. When I know I've got a warped sheet or a tricky hold down, I'll double the air flow by kicking in the secondaries. At my altitude, 5-6" of mercury is about all I get. Secondaries will boost the pull by an inch or so, but what's really going on is the volume of increased air flow adds muscle to compensate for the lower pulling force.

Glad things are working well for you - this is one aspect of the CNC process that never ceases to amaze me and is well worth all the trouble to set up. After a few jobs, you'll be very comfortable with it's use, and grow to rely on it without much concern.

jeff

[aschutsky]

I have yet to install the top lid and separator on top of the intakes since I wanted to keep an eye on things, but will do shortly. The exhaust is indeed being routed down through the side baffles which kicks out some serious heat! This weekend I'm going to ditch the filter box, install the top baffle piece, and get rid of one more 90 degree fitting in my piping. :cool: I'll also be doing my first job with 2 full 4x8 sheets. Stay tuned.

Thanks for the tips so far - it's definitely a very fun adventure playing with vac setup.

[80grit]

I just finished my vac box with 4 230v LH motors. I'm getting at least 6" of vacuum. I've got a fan blowing across the motors to assist in the exhaust cooling. I bought on of those indoor/outdoor thermostat monitors that goes up to 158 degrees and epoxied the sensor the one of the motor housings. After about 2 minutes, it maxes out at 158. So, I shut it down. The shop temp was about 88 at the time.

I had been searching here about safe operating temps for the motors, but it have seen a wide range of temps. I don't know if I need to get another thermostat with a higher max or beef up my cooling.

[Tim Lucas]

I have 2 of the LH motors and called them about the temp, they told me 180 degrees is not bad, but not to exceed that by much

I have been keeping the to cover to my box off but do not have any cooling fan assisting and my temp runs 160 - 180

[80grit]

As it approached 150, the rate of increase was definitely starting to slow down, but it's hard to say where it tops out. Looks like I need to get another thermostat.

My cooling fan is only about 240cfm. I wanted to try to be close to the volume the blower cooling fans move (60 each). I didn't want to create a big imbalance. I also ran the cooling exhaust outside to keep that heat out of the shop. I can easily remove it in the winter to help heat, if need be.

[jTr]

Tim and 80Grit:

Gary's initial forum posts about the black box is where I learned 114 is average temp for his system. I followed his directions for box construction fairly consistently and experience the same average. I panic when I start seeing 125-130, (and that's fairly rare) but never have exceeded that. My system is in year 4 now and those motors are still going as strong as day one.

If you're cooking that hot (150-180 +, especially if you've got additional cooling fans employed), you may need to go back to the drawing board and be certain the vac intake/exhaust pathway is properly separated from the motor cooling intake/exhaust path. These are two completely different air flows that must be separately routed through the box structure so the blower can pull vacuum properly while the motor's integral cooling fan regulates it's operating temp.

Forgive me for sounding overly critical, but those numbers suggest something needs to be re-assessed inside the box.

[80grit]

My box is very similar to Gary's, in that the cooling intake, cooling exhaust, vac intake, and vac exhaust are all compartmentalized and separated. The only fundamental difference is that, instead of having my cooling exhaust flow out of a baffled chamber down to the floor, mine is being pushed across the motor compartment lengthways and vented outside. I wanted to add the supplemental cooling fan, since I live in a hot climate (95 degrees today).

Where is the ideal place to measure temp? Looking down on the LH motor, there are a couple holes in the aluminum housing. One of those almost perfectly matched the thermostat sensor, so I reamed it out a little and glued the sensor inside.

[80grit]

Are these things supposed to throw a spark out of the motor when turned on? All 4 of my motors will throw a spark out of the motor when first turned on about once every 3 or 4 starts. It's quite concerning.

[David Iannone]

80grit
can you post any pics of your box build in progress?

as for the Sparks, my motors are totally enclosed in the box, so when I flip the switch I have no idea if they spark or not.

did you use the foam spacers between the vac port on the motor and the wood?

Dave

[Davo]

Off topic heat question - my router gets pretty hot on the metal round casing, specially on the collet when doing profile cuts - this normal?

[80grit]

Yes, I used the foam spacers provided.

I posted picks of my box in another thread here:

http://www.talkshopbot.com/forum/showthread.php?21679-Lighthouse-motors-running-hot

[80grit]

I'm considering incorporating an AC condenser (heat exchanger) into the cooling intake and cycling cool water thought it to help cool the air going into the motors.

I'm just trying to come up with ideas and try to fully understand what is going on withing the system. Is it correct to assume that all of the heat is generated in the motor itself and passed into the aluminum housing, thereby heating the vacuum exhaust? If my logic is correct, then the required bleed holes don't cool the motors so much from an air movement standpoint. They help reduce the load put on the motors when the table air flow is reduced. Does that make sense?

[gundog]

I don't get why everyone puts them in a box? I have always mounted mine out in the open so the air can circulate around them and they don't trap heat. I just don't see any advantage unless it is noise but I put mine outside the building and can barely hear them in the shop. (light house motors)

Mike

[knight_toolworks]

I don't get why everyone puts them in a box? I have always mounted mine out in the open so the air can circulate around them and they don't trap heat. I just don't see any advantage unless it is noise but I put mine outside the building and can barely hear them in the shop. (light house motors)

Mike

noise they are about 110db on their own very loud. though the lighthouse motors you can't seem to quiet them down much compared to other 220v motors .in the same box my other 220v's are about 87dbs the lighthouse about 95. now my blower that just died was 85 dbs and did not have that whine to it.

[80grit]

Using an IR thermometer, after about 5 minutes of running with the cover off, the outside of the housings were reading around 130-135 degrees. The inner part of the housings were reading 165-170. The copper coil exposed near the base of the motor part was about 185.

[jTr]

the outside of the housings were reading around 130-135 degrees.

Double check supply voltage- if mismatched, it could be contributing to the heat issues (and sparks...). I had to buy 208V motors as that is what the building's transformer delivers to my shop.

jeff

[80grit]

My supply voltage is 245V. I have 230V motors.