Thread: Boring out an impeller collar

I have a dust extractor with a flange mount, SP 3HP motor, and 13" impeller and would like to replace the SP motor with a 3P motor so I could spin it at 60Hz to get a bit more air through it.

As usual I want to do this on the cheap and have had in my shed for some time a 4HP 3P flange mount motor and I have a spare 4HP VFD ready to go. The flanges don't mate up but making an adapter plate should be easy enough.

The main problem I have is the original motor and impeller use a 24mm shaft and the replacement motor is a 28 mm shaft so the collar on the impeller will need to be bored out. There seems to be plenty of meat in the collar with part of it 57 mm in diameter and the other part 47 mm in diameter so even allowing for a new keyway there is enough there to work with.

Initially I was thinking of doing this on a lathe but the under side of the impeller had nothing to hang onto. The topside has the protruding collar but the the impeller has deep vanes that would prevent any normal lathe chuck from grabbing it. Plus I'm not too keen on working around spinning impeller blades on a lathe. The collar is welded to the impeller and thought about cutting it away and then boring it out and welding back in place but cutting it out will be a PITA and I doubt my skill level will enable me to place it back in its original location.

My next thought was to use a drill press or mill to get it close to 28mm and then a reamer to get a good fit.

One issue I can see is the keyway will cause the drill bit to jolt every time the cutting edges go past the keyway so was thinking of temporarily filling the keyway with a piece of mild steel and tack welding it to the keyway. I will also have to cut a new keyway and the remaining steel in the keyway would make it easier to do that.

Anyone have any other ideas?
Thanks

Vertical mill with boring head for hole then vertical slotter for keymade.

Easy peasy. You just need access to the machinery.

Ken

I agree, vertical mill and boring bar.

Or, pull the rotor from the motor and put it in the lathe, turn down the end.

I'd be concerned about keeping it balanced with a drill press or any other improvised approach.

It would be great if there is someone out west who could help...

Russ

Originally Posted by BobL

I have a dust extractor with a flange mount, SP 3HP motor, and 13" impeller and would like to replace the SP motor with a 3P motor so I could spin it at 60Hz to get a bit more air through it.

As usual I want to do this on the cheap and have had in my shed for some time a 4HP 3P flange mount motor and I have a spare 4HP VFD ready to go. The flanges don't mate up but making an adapter plate should be easy enough.

The main problem I have is the original motor and impeller use a 24mm shaft and the replacement motor is a 28 mm shaft so the collar on the impeller will need to be bored out. There seems to be plenty of meat in the collar with part of it 57 mm in diameter and the other part 47 mm in diameter so even allowing for a new keyway there is enough there to work with.

Initially I was thinking of doing this on a lathe but the under side of the impeller had nothing to hang onto. The topside has the protruding collar but the the impeller has deep vanes that would prevent any normal lathe chuck from grabbing it. Plus I'm not too keen on working around spinning impeller blades on a lathe. The collar is welded to the impeller and thought about cutting it away and then boring it out and welding back in place but cutting it out will be a PITA and I doubt my skill level will enable me to place it back in its original location.

My next thought was to use a drill press or mill to get it close to 28mm and then a reamer to get a good fit.

One issue I can see is the keyway will cause the drill bit to jolt every time the cutting edges go past the keyway so was thinking of temporarily filling the keyway with a piece of mild steel and tack welding it to the keyway. I will also have to cut a new keyway and the remaining steel in the keyway would make it easier to do that.

Anyone have any other ideas?
Thanks

Horizontal boring mill. Piece of cake. B/port type vertical mill with a boring head, ditto.

Really you could do it on a big angle plate mounted on the lathe cross slide if your lathe had enough swing. IIRC you've got a Hercus so no.

Lots of ways, depends on what you have access to.

PDW

I was at a friends place who was doing something similar. Boring with a keyway in place CAN make the hole off centred. Fine cuts will be required.
Kryn

If you can't hold it in a chuck then how hard is it going to be to hold it on the mill, do you need to make a jig to hold it?
A picture of the fan might help but l tend to agree with russ, machine the motor shaft.

Originally Posted by shedhappens

If you can't hold it in a chuck then how hard is it going to be to hold it on the mill, do you need to make a jig to hold it?
A picture of the fan might help but l tend to agree with russ, machine the motor shaft.

I though about the motor shaft but the keyway on the 28 mm shaft is 8 mm and the one on the impeller is 6mm. This would mean either cutting a 6 mm keyway in the same or different place so now its getting messy/ugly. Going the other way opens up the 6 mm to 8 mm is easier/cleaner.

The impeller is very similar to this except mine has 7 blades
ventola_etr.jpg

There is nothing on the back to hang onto and while my 4" 3 jaw can just sneak in from the blade side, that chuck is for my (small) Hercus.
I was thinking of putting the 4" chuck into the large chuck on the Nuttall or large Chinese lathe at work but that worries me a bit and I think I'd rather do it on a mill.

The blades on my impeller are riveted on so the underside is studded with rivet heads making the surface uneven. I was thinking of clamping a piece of hard wood about 20" long to the underside and drilling out dimple/recesses for the rivets to sit into. Then placing the hardwood in the mill vice? Naturally I would check for squareness etc I will definitely fill the keyway with something before I bore.

Hi Bob, you could mill the 6 mm on a 8 mm key to fit both keyways.
Cheers, shed

If you have access to a mill, then I'd say that's the preferable way to do this job, particularly if you can mount it rigidly to the board. But if I had to, I wouldn't shy away from holding that hub boss in a chuck in a lathe. If using a 3 jaw (as you say you have), shims under the jaws could be used to centre it.

If the blades are riveted, can you drill out the rivets to get a cleaner hold down in the mill?

Graham.

Originally Posted by Oldbikerider

If you have access to a mill, then I'd say that's the preferable way to do this job, particularly if you can mount it rigidly to the board. But if I had to, I wouldn't shy away from holding that hub boss in a chuck in a lathe. If using a 3 jaw (as you say you have), shims under the jaws could be used to centre it.
If the blades are riveted, can you drill out the rivets to get a cleaner hold down in the mill?

It would be possible but I think I would have to get the impeller rebalanced after replacing the rivets.

I use a chuck held in another chuck regularly, keep the speeds down and you are fine. I'd just bore it out in the lathe slowly and gently.

This shows the front side with the 4" chuck attached.
I have to use outside jaws on the 4" as the inside

I'm not even sure the lathe at work can grab the 4" as it sits below the vanes.
I also think that lathe only has a 12" swing and its a 13" impeller although I think it has a bed gap capability.

IMG_2997.jpg

This shows how little purchase the small chuck has on the collar.
I realize the main force is inwards while boring will be towards the chuck but I'm still worried about it.
IMG_2996.jpg

This shows how messy the underside is.
To support it if I use a mill, I will have to drill holes in the support material to recess the raised area around the collar itself as well as any rivets that contact with the support piece.
Or I could lay out some steel flat bar in a radial pattern that is just thicker than the raised area around the collar and rivets?
IMG_2998.jpg

Bob,

There is plenty of area between the rows of rivets for this surface to sit on parallels. There is also room around the boss for a precision circular parallel. On a milling machine you only need enough clearance on the underside for the boring bar to safely pass through. The impeller would be held down with long hold downs on the top surface. The keyway could also be cut on a shaper. Some creative thinking would be required to make a vertical fixture plate with a hole in the middle for the shaper table.

Ken

That impeller looks like it's something from the Titanic!

Yes, not much to get hold of, but at least it's against the face of the jaws. Just run it slow and take your time.

Good luck.

Graham.

Originally Posted by Oldbikerider

That impeller looks like it's something from the Titanic! .

Yes it does, but it's a 2011 dated machine.