Shopsmith Forums

As a general statement: I have ceased to concern myself with the DC-3300. I now have a DC=6000 to worry about because I have once again removed the Motor and Fan Housings from the Main Housing. I went one step further this time and detached the Motor Housing from the Fan Housing.

Having done that, I believe I have answered my question about the motor and Fan Housing being sealed where they interface. I have not removed the fan and motor but I believe I see a rubber seal between the motor and fan housings. With that I conclude that cooling of the motor is NOT dependent on air flow from within the FAN housing. Whatever cooling it gets results from air movement around the motor within the Motor Housing and threw the grated opening to the outside. This also necessitates a good seal around the Motor Housing where it meets Main Housing.

I definitely do not have that seal. I have destroyed my gaskets by excessive removal and re installation

dusty wrote: ↑Sat Aug 28, 2021 8:33 am As a general statement: I have ceased to concern myself with the DC-3300. I now have a DC=6000 to worry about because I have once again removed the Motor and Fan Housings from the Main Housing. I went one step further this time and detached the Motor Housing from the Fan Housing.

Having done that, I believe I have answered my question about the motor and Fan Housing being sealed where they interface. I have not removed the fan and motor but I believe I see a rubber seal between the motor and fan housings. With that I conclude that cooling of the motor is NOT dependent on air flow from within the FAN housing. Whatever cooling it gets results from air movement around the motor within the Motor Housing and threw the grated opening to the outside. This also necessitates a good seal around the Motor Housing where it meets Main Housing.

I definitely do not have that seal. I have destroyed my gaskets by excessive removal and re installation

I can confirm there is definitely a rubber seal between the motor (but not the motor housing) and fan housing. It also necessitates a good seal between the perimeter of the motor housing and the fan housing, what I circled in this post: viewtopic.php?p=287437#p287437 In other words, the interface that you did disassemble when you removed the Motor Housing from the Fan Housing

- David

I do not understand the concern about a gap between the Fan Housing and the Motor Housing. If air does move through that interface it is air put in motion by the fan drawing air in from the Manifold (dirty air) and depositing within the dust collector. That interface, even if it does leak, carries dirty air from outside to within the collector (the intended destination). It would not even effect the CFM.

Am I missing something?

dusty wrote: ↑Sat Aug 28, 2021 9:25 am I do not understand the concern about a gap between the Fan Housing and the Motor Housing. If air does move through that interface it is air put in motion by the fan drawing air in from the Manifold (dirty air) and depositing within the dust collector. That interface, even if it does leak, carries dirty air from outside to within the collector (the intended destination). It would not even effect the CFM.

Am I missing something?

Dusty,

The fan housing area should be under high pressure because of the fan/impeller spinning correct? So, any gaps, as David showed, between the fan housing and the motor housing will result in dust laden air from inside the DC-3300 migrating to the outside through this motor housing compartment. The reason for this is that gases move from high pressure areas to low pressure areas. Inside the fan housing is high pressure and outside the DC-3300 (or inside the motor housing) is low pressure. Essentially it will be an air leak causing dust to exit the DC-3300 which is undesirable.

RFGuy wrote: ↑Sat Aug 28, 2021 8:20 am

DLB wrote: ↑Sat Aug 28, 2021 8:13 am

dusty wrote: ↑Sat Aug 28, 2021 5:13 am
Is there a cooling fan on/in the back side of the DC-6000 motor?

Please clarify. Are you asking if there is a second fan, besides the one that's exposed? Or did you mean DC-3300?

-David

Isn't Dusty talking about this fan?

The answer IMO is that it has part of a cooling fan. The motor design is similar to the popular Totally Enclosed Fan Cooled (TEFC) Motor. The difference I see is that a TEFC motor has a cover over the centrifugal fan. One of the purposes of the cover is to direct the (cool) air flow from the fan over the (warm) case of the motor to cool it. I've already admitted to limited knowledge of fluid dynamics, but some of it is within my grasp and I had occasion from time to time to work with some experts that did little else. On a centrifugal fan, air enters axially near the center and is accelerated outward radially (somewhat inefficiently without the cover). This fan is of smaller diameter than the motor end cap, so I reckon most of that air will go outward in the available directions toward any area of lower pressure and not in the direction normally associated with a TEFC fan. IMO that means a lot of recirculation and a lot of air escaping out the back through the grate and not very much cooling other than the rear endcap of the motor.

(Notes - I did a fair bit of searching and did not find another motor with an exposed fan to compare. Because a centrifugal fan/impeller almost always operates inside a chamber, I'm making some assumptions here that are definitely beyond my expertise for how it is going to behave when most of the chamber is not present. I think my assumptions follow basic physics. And are consistent with observations of my machine's behavior, both unsealed and somewhat sealed. Measuring actual airflow from just the fan would probably require sealing all leaks into the motor housing.)

- David

If I was putting my DC-6000 together today for long term use I would make two changes. 1) I would 'permanently' seal all known or suspect leaks so the dust stays collected. 2) I would semi-permanently add a thermocouple to the top of the motor so that I could monitor temperature when I felt it necessary or useful. The latter would help me manage the duty cycle on the assumption that as designed the machine is not suited for continuous use (as I believe). The thermocouple should be carefully routed through the grate and away from the fan, not difficult as there are two other cables already there.

I'm holding off on this in the expectation that the MS may want to RMA my motor housing, and/or perhaps eventually provide me with a replacement. I'm instead going back to the 3300 for now because I need a working dust collector. I may also decide to do the above with non-permanent seals.

I did not collect enough thermal data to have a reasonable guess at a duty cycle for the DC-6000. I'd adapt RFGuy's 175F - 200F range, probably 200F, as a guide, as that range is consistent with other information I've seen. In my instrumented evaluation the machine reached 175F+ in 20 minutes and 200F+ in 30 minutes. I started from a shop ambient near 83F. The machine was at ambient, had not been run since the day before. So 30 minutes continuous would be an upper limit starting from cool. Subjectively, the machine takes a while to cool down.

- David

What air pressures are resulting from the fan on the rear of the DC-6000?

Air will be drawn in at the center of the fan and expelled outward.

This creates a lower pressure at the center of the 'grill area' and greater pressure at the periphery of the fan rotor.

I think some of the pressure causes some air flow forward towards the DC blower end of the motor.

The flow will pick up some heat from the motor case fins.

At some point that forward flow will cease.

Now that additional increased pressure at the back(fan) end has to go somewhere else. I think it will simply go out the back along the outer edges of the motor box. That flow will also pull the heated air from the forward flow ceasing point.

This would explain the higher temps at the blower end of the motor.

I think a lot of wishful thinking going into this 'design'.

It would likely cool better IF there were a vacuum leak near front of the motor that allowed the motor box air an exit.

JPG wrote: ↑Sat Aug 28, 2021 2:26 pm What air pressures are resulting from the fan on the rear of the DC-6000?

Air will be drawn in at the center of the fan and expelled outward.

This creates a lower pressure at the center of the 'grill area' and greater pressure at the periphery of the fan rotor.

I think some of the pressure causes some air flow forward towards the DC blower end of the motor.

The flow will pick up some heat from the motor case fins.

At some point that forward flow will cease.

Now that additional increased pressure at the back(fan) end has to go somewhere else. I think it will simply go out the back along the outer edges of the motor box. That flow will also pull the heated air from the forward flow ceasing point.

This would explain the higher temps at the blower end of the motor.

In my experiment the higher temps were at the cooling fan end of the motor.

I think a lot of wishful thinking going into this 'design'.

I kinda wish I had waited a little longer to jump on this particular bandwagon.

It would likely cool better IF there were a vacuum leak near front of the motor that allowed the motor box air an exit.

My thoughts too, for when the thermocouple thing shows an irritating sort of duty cycle is needed. If the 4" coupler were replaced with something with a "T" such a leak could be routed around the impeller housing through flexible hose. With a properly sized leak one could eliminate the cooling fan and re-allocate its intended purpose to the impeller. We might lose some CFM but that seems a small price to pay, considering. Right now I'd be guessing at the hose (er, leak) size needed, any ideas?

- David

When you say a vacuum leak near the front of the motor that would allow motor box air an exit I have to ask - What is the grill in the Main Housing? Air comes out of that grill with some gusto and it is warm. Definitely warmer than ambient so it is carrying off some heat. from the motor.

I would be curious what a temperature profile exists at different positions at the 'grille'.

I presume near ambient temps at the center and heated air at the outer areas.

I think air pressure is low at the center and higher at the outer areas.