Thread: DIY inside grinding attachment for cylindrical grinder, what design?

Originally Posted by Mr_CNC_guy

Don't enclose the motor too well, it needs to be cooled!

I spent a few minutes looking at possible fan locations. Remember that I intend to enclose everything within a cover.

I first thought about having the fan as below. The airpath is shown with the blue arrow. Cold air would be sucked in by the fan, would run upwards by the motor, and then would exit through vent holes on the right side of the shroud next to the motor pulley. In use this would work well because the air inlet would be facing the operator and well away from the grinding mess. The downside is that when the internal grinding attachment is rotated up and out of the way, then the air inlet would be facing directly upwards on the top of the outside grinding head. That's not good, it would fill up with coolant and grit. Yes, I could make a cover for it, but I'd forget to use it



Maybe a better way to do it would be to mount the fan directly BELOW where I am holding it, onto the back plate. I could mill an inlet louver into the back plate, with slots opening downwards at 45 degrees. That location should be well protected against the coolant and grit mess. Then when I rotate the inside grinding attachment up and out of the way, the fan opening is facing downwards, and is underneath the attachment rather than on top. That plus gravity would keep stuff from getting inside.

The only downside I can see to this is that I would have to mill a bunch of air inlet slots in the back plate, which would make that plate more flexible and less rigid. Not sure if that matters, since the whole point of grinding is to keep the forces low.

An alternative would be to mount the fan onto the outside of the cover on the right by the drive belt. That's well protected against coolant and grit ingress, but also means that removing the cover requires disconnecting wiring. I suppose if the cover hinged up that would not be so bad. But having the fan outside the shroud also puts it into a vulnerable location for damage compared with being mounted on the backplate.

Decisions, decisions....

Actually I like the idea of a cover that hinges up for access to the inside. One less thing kicking around on the bench during setup. I might try this.

^ The high speed Heald grinding heads blew an oil fog through the unit to cool and lubricate the bearings.

@ZK, you could always buy a container and park it out back

Most /all newbies try to make massive cuts like a lathe.....both internal and external.....all wrong......the motor should be supplying fractional horsepower,and and the wheel making just a tiny display of sparks ......not a stream like a Makita....I have always used water based coolant with internal grinding,and never had an issue with chatter or burning.

Heald grinding heads

These folks must of been dead serious about ID grinding - I have the guts out of a fair sized RED HEAD. The hefty spindle has a short B&S 12 ID taper (1.797" big end) on the business end and the 2MM precision bearings are the 211 size. The casting that held all this machinery had to weigh 30 Lbs each

Originally Posted by cameraman

yup , now they pop into existence whereas before if I hit refresh and wait etc. the images don't 'Lay up" to the page ?

Anyhoo lol.

So I just reply and, presto!, the photos appear?

Lo! It is a miracle! I can see!

Not related exactly, but...
I have a Brown Sharpe #13 grinder that I want to install an internal attachment on.
On ebay I found a spindle (2 spindles actually) that were originally made to fit
a Cincinnati #2 tool-cutter grinder. They are belt drive, and I think the taper
is a #6 Brown Sharpe with 5/16-18 LH thread drawstud. I am going to fab a steel
bracket and drive it with a flat belt from the right side of the main spindle.

I also have a Heald #7 ID grinder that I am going to completely fix up some day.
I think it is from the 1930s. Originally overhead driven for sure.
If the plain workhead bushings are good and the ways look good (when I take the
table off), it should make a fine machine. It has a Parker (pre-Majestic??)
spindle cartridge, that mounts with a dovetail, just like a RedHead spindle.
I was thinking I might buy one or more RedHead spindles off ebay if I see them
cheap, but I need to assess the machine better first. I must say this Heald is
a work of mechanical art. Very massive construction, should be very resistant
to chatter. They really put all their efforts into this machine when they
designed it.

--Doozer

I didn't like the first version of the cover and threw it in the trash. Now working on version 2. Basic idea is to enclose as much as possible. So on the grind side all that is going to be visible is the spindle protruding:



Yeah, it looks like a box, but if I end up with a cover like this I'll round out the corners so it matches the machine underneath.

On the tailstock side I'm mounting a pair of 92mm/3.625" fans. The bottom one (left in photo) will blow in cold air above the spindle and below the motor, and the top one (right in photo) will suck out the hot air just above the motor.



I'll put grills onto the fans to protect against fingers. My expectation is that on this side and in this location they will be reasonably protected from the mess. Also easy to keep an eye on them.



The cover will hinge up more than 180 degrees and will then just rest in position out of the way. Just now it's blocked by a piece I added to extend the range over which I can move the motor up and down to accommodate larger and smaller pulleys. That's on the list of things to fix. That way I can change pulleys or spindles with two rather than three hands.

I'll run the fan wiring with flex cable so that the wiring won't need to be touched when opening/closing.



Here it is locked in the "out of use" position. I've left just enough clearance underneath for the handle which moves the cross slide back and forth.



Next step is to see if I can get the electronics fitted inside, rather than mounting them outside. IMO that's preferable, to keep things compact.

Still need to figure out a safety hook or latch to retain this in the "up" position even if the hinge shaft comes loose.

I also need to give some thought to how to fabricate/reinforce/brace the cover so that it doesn't vibrate or resonate.

Still too busy to spend much time on this. Here is how the mock-up currently looks from the outside. Botton fan blows air in and the top fan pulls air out:



Here is on the spindle side. Nothing is exposed apart from the spindle itself.



For the inside, the drive electronics is going to sit on top near the exhaust fan. It has a temperature sensor inside so if it gets too hot in that location it will shut things down. The controls for speed/on-off/CW-CCW will be accessible at the top when the cover is closed.



Next step is for me to get the wiring and controls laid out. Only things running into the box will be 48VDC power and a piece of 1/4" clear flexible tubing to carry compressed air/oil fog to high speed spindles. I've also decided to change the motor mounting so that I can tighten it into position entirely from the operator side. Finally need to add a "security hook" for locking the assembly in place when swung up and not in use.

I might also add some "stiffeners" to the cover inside, laid out to direct cooling air in the correct places.

Hi Ballen:
I've been looking at where this thread is going, and I have a really basic question to ask you about your design.
You've designed your unit with an enclosure...I presume to keep the dirt and grinding swarf out of the guts .
Then you punched a pair of big holes in it and made a system to pull the dirt and swarf right through the parts you were guarding.
This strikes me as fundamentally wrong.

As an alternative, have you considered enclosing the dirt-sensitive guts in a heat sink and blowing the fans over that instead? (Kind of like a TEFC motor is constructed)
It would seem to make some sense, however you'd need to find a convenient way to access the heat sink so you could clean it from time to time, especially if you intend to run the grinder with coolant.

To get an appreciation of my concern, open up your shop computer some time and see how nasty it has gotten in there, from the fans sucking in ambient air all the time.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

Hi Marcus,

Thanks for the comments!

It's a good question. I am hoping that by putting the fans on the far right hand side, away from the grinding mess and activity, they will not pull in gunk. And even if they do, I have a "plan B" which is to add some standard filters to the fans. If that doesn't work, then turning the cover into a big heat radiator is certainly an option. Or adding some cooling coils and running coolant through the coils to carry heat away.

Yes, I am familiar with the enormous dust bunnies that can be found inside of computers and laptops. If this attachment was going to be operating 8 hours/day then it would be a valid concern. However this machine is not used for production, it is entirely for one-off parts. So I might end up running the ID grinder for 10 hours/year.

I got to spend a couple of more hours on it today adding the wiring and controls. The top will have a power switch and LED power indicator, and the LCD motor speed display and potentiometer knob. I also have a 3-position toggle switch which will be for CW/OFF/CCW rotation. Initially I had planned to put this on top but I now leaning to putting it inside next to the spindle. The idea being that one never touches it except when the spindle is being changed. So getting it off the top where it might be bumped accidentally seems like a good idea.

Hopefully the model will be finished tomorrow and I can turn to building the real thing. I'll post some more photos when the model is ready.

Cheers,
Bruce

PS: input power to the box is 48VDC at up to about 10 amps. Can anyone recommend a 3-pin power connector for bringing the power/ground in? The connector should be reliable, splash-tight, compact, and have a good locking mechanism, like LEMO connectors.

OK, prototype is just about finished. Here is the wiring:

48 VDC comes in the back along this white cable from a switching power supply:


Electronics is in the top of the cover:

On the left is the drive for the brushless DC motor, on the right is a 48V-12V buck downconverter to provide power for the fans and the LED indicator light.


It's a bit tighter for space than I anticipated, so in the real thing I am going to make the unit 3cm higher and 1cm deeper.

Here's the operator view:

The rotary switch is on/off power, green LED is a power indicator. I think I am going to add a spindle on/off with a CW/CCW selector under the cover.

Spindle side view:


Front view:


I just discovered that the upper fan is interfering with the cross slide coarse adjustment lever, need to move things up another 2cm: