Thread: Fan Modification.

BaronJ, there is far too much restriction of air on your alterations. Looks good, but you need to open those small holes right out and I would cut the louvers away where the fan is located. You will notice a big difference in air flow when you do it.

Regards,

What sort of mill is it?

Originally Posted by Wimmera Jack

I would cut the louvers away where the fan is located.

I think he has(or at least most of them), though some of the pictures seem to be from the mock up stage.
I guess if its better than it was, maybe it will be good enough, but like you I'd like to see the little holes gone. maybe cut the top out and fit the grill then make up a "duct" to top swarf getting in. Though I've got no idea what mill this is off so maybe its not doable?

Stuart

Looks like a BF20 type clone, maybe a Titan branded one.

Anyway, I agree with the others, I'd open that top right up and do away with the tiny holes. Just not enough open space there to really achieve what you are trying to achieve. If you think you might have swarf problems getting in there do as Stustoys says and fabricate a duct type set up to just cover the top and draw from the back, that chrome guard does nothing.

I have just received a BF20L and only last night got it into its stand/enclosure so I'll keep an eye on the temp of the motor. I'm almost ready to start making something.

Hi Guys,

I'll try to answer all the questions in this post.

The reason that I didn't drill larger holes or cut away the top was so that I could analyse the airflow pattern and add more holes as needed. Who was it that said measure twice. In actual practice I did add another series of holes roughly doubling the apature size.

Because I found that air escaped through the louvres only passing up the rear of the motor and not through it, was the reason for blocking them up. The idea was to force the air path to flow all around the motor and the tiny fan in the motor would guide air up through it. (I pulled the fan off the shaft and turned it around. A spot of super glue was needed to make sure that it didn't slip down due to vibration.

Additional information !
The motor is a DC permanent magnet one with current fed through the armature via carbon brushes at the top. Its also 110/120 volts and not 230/240 as would be expected for use in the UK. I have more info about this motor that I'll leave for now.

As far as who actually manufactured the machine I don't know and the supplier won't tell me. I can provide some photographs of the machine, however at the moment I would rather not Identify the supplier. It seems that several UK companies import and badge this machine for themselves. I did mention that I have had some issues with this machine, all concerning manufacturing. To give the supplier their due, in the first instance they unhesitatingly offered to replace and refund me, collecting the machine at their cost if I wished. In hindsight I should have taken up their offer.

Originally Posted by BaronJ

Hi Guys,
I pulled the fan off the shaft and turned it around. A spot of super glue was needed to make sure that it didn't slip down due to vibration.

BaronJ,

If the fan is of conventional design with fixed pitch blades, turning it upside down will not normally reverse the airflow - it will still deliver air in the same direction, but usually less efficiently. The only way to reverse the airflow with a conventionally designed simple axial flow fan is to reverse the shaft rotation.

Visualise a spot near the tip of one fan blade, and the path of the airflow past it. The spot on the fan blade is following a path through the air similar to a spot on the thread of a bolt being screwed into a nut, or, conversely, the air mass is being "screwed" past the bolt. Remember when aircraft propellors were originally called airscrews because of the way they "screwed" their way through the surrounding air? If you turn a right hand thread nut upside down you don't then have a LH thread nut - you still have a nut which will screw onto your RH thread bolt using the same clockwise rotation.

Regards,

Frank.

Hi BaronJ,

Nice job, I hope it keeps it's cool...

FWIW. You can get those same fans in 240V versions, that is assuming you can't find 12V inside the machine. The quality varies a fair bit, some have better bearings, the best have ball bearings.

Regards
Ray

"I pulled the fan off the shaft and turned it around. A spot of super glue was needed to make sure that it didn't slip down due to vibration."

As another poster said, all you have achieved is a lesser flow of air.
Just turn the whole fan over to get the opposite air flow.

Super glue will now cause you some problems.

Regards,

Originally Posted by franco

BaronJ,

If the fan is of conventional design with fixed pitch blades, turning it upside down will not normally reverse the airflow - it will still deliver air in the same direction, but usually less efficiently. The only way to reverse the airflow with a conventionally designed simple axial flow fan is to reverse the shaft rotation.

Visualise a spot near the tip of one fan blade, and the path of the airflow past it. The spot on the fan blade is following a path through the air similar to a spot on the thread of a bolt being screwed into a nut, or, conversely, the air mass is being "screwed" past the bolt. Remember when aircraft propellors were originally called airscrews because of the way they "screwed" their way through the surrounding air? If you turn a right hand thread nut upside down you don't then have a LH thread nut - you still have a nut which will screw onto your RH thread bolt using the same clockwise rotation.

Regards,

Frank.

Arrg ! Yes your right !

It just never occured to me. I ran the new motor on the bench from a 12V supply and it blew air out of the bottom. Two bolts and five minutes I had the motor apart and the fan pulled off. It came off just by pulling it with my fingers, thats why I spotted it with super glue when I pushed it back on.

Looking at the old one The fan looks quite symetrical except for the swage, which on the new one now looks the other way.
I should have twisted the blades to face the other way.

Thanks Frank.

Originally Posted by RayG

Hi BaronJ,

Nice job, I hope it keeps it's cool...

FWIW. You can get those same fans in 240V versions, that is assuming you can't find 12V inside the machine. The quality varies a fair bit, some have better bearings, the best have ball bearings.

Regards
Ray

Yes I have a couple of 220/240 Volt ac ones. I didn't fancy having AC mains voltage up top. The fan I fitted has one ball and one sleeve bearing I think.
As an aside some of these fans have very useful ball races in them around 8 or 10 mm diameter. Some fans that have sized up and been taken apart have a perfectly good ball race ! It seems that the sleeve bearing is the one that sizes up.

Thanks Ray.

I think you'd be best leaving it alone.

Pushing air or pulling air through the motor won't make any actual difference. You're still dealing with the same motor rpm and blade pitch so you wont be doing anything in terms of increasing the air flow. If you go bending anything you're just going to end up putting things out of balance.

Might be time to just trust that the manufacturer knew what they were doing when they designed the motor.

Adding your fan on the outside will no doubt help but I'd leave it at that.

Just another thought.

When you burnt your motor up what speed did you have it running and how big was the cut you were taking and for how long? High or low gear?

With these variable speed controllers it can be tempting to just dial in whatever speed you want and think it's going to be ok but generally these motors like to run on the faster side. If you were running it slow you might have been overloading the motor and drawing a high current, coupled with the reduced rpm decreasing air flow and you get your over heating issue.

Just saying it might be how you are using it that is causing the problem?

If you want to add additional fans for cooling this type of fan can be bought for a few dollars quite readily. They are the same type as used in your PC, which is another source if you look at the hard rubbish for a freebie.

Hi Guys,

A bit more info about this modification. As the machine was originally made the motor is bolted onto a rectangular steel baseplate about 20mm thick with the housing enclosing the whole base. Apart from the louvres in the housing there is no place for air to get in or out. Since the louvres point downwards at the back, the top of the housing collects the heat and then air circulation virtually stops. Taking the cover off the mandrel where the drawbar is allows some heat to escape. Indeed removing the whole housing is a great improvement cooling wise. However that leaves the top of the mandrel exposed along with the spindle speed sensor. A potential injury hazard. Plus is isn't very pretty. The fan certainly does what is intended and the air flow keeps the motor relativly cool.

The motor itself is a permenant magnet type with the magnets, one on each side of the armature, restricting the airflow through the motor. All the heat produced is from the armature windings. There is no heat generated by the magnets themselves only radiated heat from the armature and conducted heat via the steel shaft and bearings.

A comment about the vent holes.
I monitored the air temperature coming out and added extra holes to increase the through flow of air. The idea is to restrict the airflow enough for it to pick up the maximum amout of heat and carry it out of the vent. If the airflow is too high then you don't get all the heat you can out. The other consideration is dirt and dust falling into the motor housing.

Originally Posted by BaronJ

Hi Guys,

The idea is to restrict the airflow enough for it to pick up the maximum amout of heat and carry it out of the vent. If the airflow is too high then you don't get all the heat you can out. The other consideration is dirt and dust falling into the motor housing.

The greater the airflow, the better the cooling. Trust me.

Regards,