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Hamilton Sensitive Drill Press pulley replacement.

noynac

Plastic
Joined
Jun 19, 2023
I have a Hamilton sensitive drill press, but the pulleys are worn, and while one is still attached well, the other is very loose.
I don't really know where to begin trying to replace it, I see mcmaster & similar sites offer a wide range of u groove pulley sizes, so I may just be able to order one from there. However, I also am not sure how to go about removal and fitting. I don't see any type of set screw / key, so I assume it is press-fit. Any suggestions are appreciated.
I have attached an image of the drill press, as well as a short 20 second video of the pulley in question.
The belt runs along the in-side channel you can see in the video. About 1/5 feels like smooth plastic, the rest feels like a thin layer of rubber.
On the opposite side with the pulley that is firmly attached, this channel is completely smooth plastic-feeling.

IMG_8737.jpg
 
Here is better picture of the pulley/belt configuration, since you can't see the second one from the picture or video I posted.
IMG_8766.jpg
 
I see several manuals on Vintage Machinery. Unfortunately the drawings suck. I blew up this one and it looks likely they have a pin or set screw under the belt. chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/http://vintagemachinery.org/pubs/1979/26952.pdf
 
I see several manuals on Vintage Machinery. Unfortunately the drawings suck. I blew up this one and it looks likely they have a pin or set screw under the belt. chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/http://vintagemachinery.org/pubs/1979/26952.pdf
After looking around the bottom, I did find a set screw at the center. There doesn't appear to be anything near the pulleys themselves, just one directly in-between.
However, even after removing the set screw, the pulleys do not budge. At least, not with manual strength.
Is it possible it is press-fit tightly in addition to the set screw? I am assuming the set screw has something to do with the pulleys at least, since there is nothing else around that area for it to be for.

edit: I have found the drawings for this model from the site listed: here it is
Still unsure how to remove though.
 

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From the drawing, it looks to me like there are dust covers on the outside hub of these idler wheels. I would start by thoroughly cleaning them so you can actually see what you are dealing with. It looks to me from the picture that there is a small notch where a small screwdriver is used to remove the dust cover. Inside I would expect to see a clip ring that captures the bearing to the shaft.

But before you disassemble it, you should have some sort of plan as to what you intend to do about it. These are just idlers to change the direction of the belt, they aren't actually transmitting any real forces like the drive pulley or the chuck. Assuming the internal bearings are good, some basic polyester filler or epoxy to fill any divots and some careful sanding should be able to smooth out any serious variation. A rubber liner made from a bicycle inner tube or thick rubber band could help as well. Replacement idler wheels, if you can find them, are unlikely to be cheap.
 
Looks to me like there's a 'dust cap' in the pulley hub that hides the circlips/snap rings that retain the bearing on the shaft & the bearing in the pulley. The dust cap might be a bugger to remove intact/undamaged, may have been considered expendable. Maybe try prying it out with a small thin bladed screwdriver .. sharpen one if necessary.
Duhh .. beaten by Baka!
 
From the drawing, it looks to me like there are dust covers on the outside hub of these idler wheels. I would start by thoroughly cleaning them so you can actually see what you are dealing with. It looks to me from the picture that there is a small notch where a small screwdriver is used to remove the dust cover. Inside I would expect to see a clip ring that captures the bearing to the shaft.

But before you disassemble it, you should have some sort of plan as to what you intend to do about it. These are just idlers to change the direction of the belt, they aren't actually transmitting any real forces like the drive pulley or the chuck. Assuming the internal bearings are good, some basic polyester filler or epoxy to fill any divots and some careful sanding should be able to smooth out any serious variation. A rubber liner made from a bicycle inner tube or thick rubber band could help as well. Replacement idler wheels, if you can find them, are unlikely to be cheap.
You were right!
So I could potentially just fill it around the area that is moving freely horizontally?
Though, it would still be ideal to replace the idler wheels.
 
If you can find and afford new idler wheels, or have the skills and equipment to machine new ones, then by all means replace them. The idlers serve three purposes here, the belt direction change, tension adjustment and to help align with the different sized drive pulleys. If they are still effectively doing those tasks, then leaving them alone (despite their looks) is best.

From the pictures it looks like it was perhaps over tensioned and with a belt that may have been contaminated with dirt and other abrasives causing excessive wear of the softer material they are made from. There appears to be a pair of grooves worn into it which I could see causing issues where the belt might hunt between different diameters causing the belt tension to vary excessively, but I'm only speculating, you should tell us what the actual issue you are having with them is.

EDIT:

Looking at the video, I think your concern is with the idler shifting on the bearing. The bearing itself doesn't have the circlip would expect to see that would keep it from coming off of the shaft, and that play indicates to me that that's exactly what it has done. Try tapping the bearing tight on the shaft using a socket that only contacts the inner race. That will remove the slop of the idler. I expect there will be a groove in the shaft for a snap ring, measure the groove and buy and install the correct ring. If there is no ring and the bearing works its way loose again, then Loctite 638/648 bearing retaining compound will keep it in place.
 
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Yes, that is my main concern is the idler shifting on the bearing. There is a snap ring that popped out when I removed the cover, and I placed it back in before putting the cover back on.
When I run the drill, that idler shifts. It not only causes there to be a bit of wobble / waviness I can see on the belt on that side, but the resistance of the pulley changes as well. It becomes harder to turn. Granted, I am not sure if that really makes a difference here, as the motor just powers through and it gets turned as fast as it needs anyways.
 
Yes, that is my main concern is the idler shifting on the bearing. There is a snap ring that popped out when I removed the cover, and I placed it back in before putting the cover back on.
Please don't leave out this kind of detail, we're driving blind here. Is this only happening to one of these idlers? The other is not moving side to side? Again, details are important.

When I run the drill, that idler shifts. It not only causes there to be a bit of wobble / waviness I can see on the belt on that side, but the resistance of the pulley changes as well. It becomes harder to turn. Granted, I am not sure if that really makes a difference here, as the motor just powers through and it gets turned as fast as it needs anyways.
Well you usually want a bearing race to have a tight fit to whatever it is seating as slipping will cause wear and lose concentricity. Some retaining compound seems prudent, however in the drawing I believe I see 2 clip rings, a smaller one that holds the inner bearing race to the shaft, but also a larger ring that constrains the idler to the outer bearing race (that would presumably keep the idler from moving side to side.) You may want to open the other side and see if it has one in place or look for the groove in the idler where such a ring would seat. Bonding it will work without that clip ring, but keeping it factory is always the smart way.
 
Please don't leave out this kind of detail, we're driving blind here. Is this only happening to one of these idlers? The other is not moving side to side? Again, details are important.

I apologize, I had first asked for help on discord, where I did include this information. I guess it slipped my mind when posting here.

The idler on the other side does not appear to have any play. It does not move when pulled outward, and rocking side to side has no wobble like the idler on the lever side. I have not removed the cap to check the better side yet. I will do it tomorrow.

And as said before, both appear to have deep worn grooves along the inside edge. The belt looks like it nearly, or just barely does, touch the side of the machine along the section in-between the idlers and the spindle. I don’t think it is close enough to be an issue or wear the belt, but it is extremely close.
 
I apologize, I had first asked for help on discord, where I did include this information. I guess it slipped my mind when posting here.

No worries, remote troubleshooting unfamiliar hardware is a little stressful. Just based on the low-res drawings I expected some form of retainer, and now that you confirmed it I took a closer look and based on the drawing expect that there is also supposed to be the larger retainer and seating groove I mentioned in the previous post.

The idler on the other side does not appear to have any play. It does not move when pulled outward, and rocking side to side has no wobble like the idler on the lever side. I have not removed the cap to check the better side yet. I will do it tomorrow.

This is very useful, as having a properly working one for comparison is extremely helpful. My expectation is that you will see 2 circlips in there. Which if true leads to the question, why was the other one missing? It could be it broke and wasn't replaced or the person just lost it, but there is a chance it was removed to allow that slip because due to wear the idler was otherwise overconstrained (a bad fix, but desperation and lack of care leads to such things.) So just replacing it may not be the permanent fix we want, but it's still the first thing to try.

The 'wobble' is not a good sign and may indicate that there has been damage from the bearing slipping in the race. Retaining compound can help, but you will lose some concentricity and you need to make sure it cures with the idler perpendicular to the shaft or you will have a permanent wobble.

In any case, repack the bearings with fresh grease while you are in there.

And as said before, both appear to have deep worn grooves along the inside edge.

Yeah, the drawings show a smooth flat profile on the new part, those grooves appear due to excessive wear, which again I speculate as a combination of a dirty belt and over tensioning. Do you have access to a lathe, or some way to turn a clean profile if you fill those worn areas with epoxy and some kevlar thread?

If I had the part I would model it and 3D print it out of nylon, you may be able to find someone willing to do that for you where you are. Turning new ones out of Aluminum or Brass would be ideal, but will be more costly. These are neat little machines, so someone may be selling replacement idlers, I haven't looked.

The belt looks like it nearly, or just barely does, touch the side of the machine along the section in-between the idlers and the spindle. I don’t think it is close enough to be an issue or wear the belt, but it is extremely close.

Yeah, the wear has certainly changed the geometry. Returning the idlers to the original shape should help with that. I would replace the belt as I suspect it is packed with abrasive grime, if so it will continue to destroy things. I think there are modern round section synthetic drive belts that will work really well (even if they may ruin the classic looks.)
 
Mine is a bit different, I think. Looks like there are no bearings, just a pin with a couple of retaining caps on either side. Possibly a bronze sleeve in the hub of the bakelite idler..I'm a big fan of those little drill presses and of Hamilton stuff. I have a couple of the double-cone tapping machines and a variamaticIMG_20230808_133907628_HDR.jpg IMG_20230808_133119902_HDR.jpgIMG_20230808_133022586_HDR.jpg
IMG_20230808_133101504_HDR.jpg
 

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Mine is a bit different, I think. Looks like there are no bearings, just a pin with a couple of retaining caps on either side. Possibly a bronze sleeve in the hub of the bakelite idler..I'm a big fan of those little drill presses and of Hamilton stuff. I have a couple of the double-cone tapping machines and a variamatic
ohh interesting, I didn't realize they made a variation with that style. How does the varimatic compare to A-M? I think I remember reading about the variable speed adjustment on another forum.

This is very useful, as having a properly working one for comparison is extremely helpful. My expectation is that you will see 2 circlips in there. Which if true leads to the question, why was the other one missing?
I have made a higher quality video in-focus and showing both sides.
Here it is:
Also, now that I take a closer look in the light, I can read the bearings are labeled Fafnir 200KD, which appear to be available quite cheap.

In addition to the video, here is an image of each side.
Wobble/Slide:
wobble.jpg
Good... well, no wobble or sliding at least:
good.jpg

I also noticed there is a portion on the wobbly one that is raised that I assume fits into a notch.
I trace around it with a blunt pick to show the area I am meaning.

Lastly, the part I thought was the clip, when taking the cover off of the good idler, I realized that the clip was around the outside of the cover, not the inside.
 
Okay, part of the problem here is that you haven't effectively cleaned these and we are looking for clues that are likely obscured by all this cruft. It is likely over the years they had various designs, I only have the PDF and the two different examples we've seen in this thread. Yours may be different from what the design shows, but it is too dirty and inaccessible to know at the moment.

Based on the drawings, this is what I would expect to see:

IDLER_Render2.jpegIDLER_Render.jpeg

My reading of their cross section shows two bearing retaining clips (unclear what type) that retain the bearing to the shaft and the idler. In your pictures there are no signs of any clips, and it appears that the inner bearing race is press fit onto the shaft (which is a kind of crappy way to do it if true.)

The two things that jump out at me are:

1) Why is there any room for the sliding Idler to even move? If the outer bearing race was slipping (something that there is a good deal of evidence for) then it is possible that it has eroded the lip on the back side of the idler that was retaining it. Or there was a spacer that has somehow disintegrated. The other one isn't moving, either due to friction against the outer race or there is enough debris packed behind the bearing it can't move. We won't likely know until this is disassembled.

2) That raised protrusion doesn't make sense unless it was there to keep a circlip from rotating, but where is the circlip groove? If it exists, it is very likely that it is hidden under the bearing which can't expose it because there is garbage preventing it from fully seating.

But all this speculation is just extra work. To do an effective repair you need to clean, disassemble, analize, create a solution, test, and repeat if required.

I hesitate to have you disassemble this now, because if that bearing is a press fit to the shaft, we know that these idlers are fragile and I suspect you don't have the correct bearing puller to attempt this without causing damage.

Regardless, the first step is to remove the belt (which is loading everything and interfering with your ability to manipulate these) and clean the ever living crap out of these guys so you have a hope of understanding what is different about them. It may be as simple as, these are all supposed to be press fits, and the bad side spun its bearing and wore out the mating surfaces. Reboring it and fitting an oversized bearing, or loctite may solve it (doubtful with that wobble) but let's get it clean and see if we can figure out what is wrong. WD40, 99% IPA and brass brushes are your friends for this.
 
I had a bunch of these over the years and still use the first one I got, circa 1939, sold to the Washington, D.C. Navy yard. It has the groves worn in the pulleys which does not effect its operation so I wouldn't get stressed over that. Yes the belt is very close, maybe touching the side casting but does not matter. Years ago I rebuilt the machine back when you still get parts from Hamilton. These bewaring were common as I recall so just replace them both. I think i had to knock them out with a pin punch because the set screw had a burr that keeping the shaft from sliding out. Since the shaft is just a steel rod you could make a new one a little longer to eliminate the belt rubbing. These machiines are nearly bullet proff and will run forever, just don't try to over complicate things. BTW, I use Habiset round green belts fused together, they last for over a decade.
 
Okay, part of the problem here is that you haven't effectively cleaned these and we are looking for clues that are likely obscured by all this cruft.
I have taken a short video with commentary.

My reading of their cross section shows two bearing retaining clips (unclear what type) that retain the bearing to the shaft and the idler. In your pictures there are no signs of any clips, and it appears that the inner bearing race is press fit onto the shaft (which is a kind of crappy way to do it if true.)

The two things that jump out at me are:

1) Why is there any room for the sliding Idler to even move? If the outer bearing race was slipping (something that there is a good deal of evidence for) then it is possible that it has eroded the lip on the back side of the idler that was retaining it. Or there was a spacer that has somehow disintegrated. The other one isn't moving, either due to friction against the outer race or there is enough debris packed behind the bearing it can't move. We won't likely know until this is disassembled.

2) That raised protrusion doesn't make sense unless it was there to keep a circlip from rotating, but where is the circlip groove? If it exists, it is very likely that it is hidden under the bearing which can't expose it because there is garbage preventing it from fully seating.

But all this speculation is just extra work. To do an effective repair you need to clean, disassemble, analize, create a solution, test, and repeat if required.
I essentially say this in the video, but from what I can tell it seems that the raised bump may go all the way across the inside of the idler wheel, and fits into a notch cut all the way across the bearing. Is it possible that the idler is press-fit onto the bearing, and the raised area w/ the notch is so it's locked into place from slipping when rotating? Looking at images of the bearing online, there are definitely no notches cut into it, so I assume it must serve some purpose, if not the one above.

The bearing itself seems to have some wobble, which I guess may be why the pulley worked it's way loose or was damaged ?
Originally I just thought that it was only the idler wheel wobbling on the bearing, but I was wrong. with the cap off, pressing gently on the outside ring of the bearing, it has play. The other side does not.

Granted, the idler wheel does still have play in addition to the bottom ring of the bearing.

One other question, what grease would you recommend I apply to the bearing? A brand or viscosity to look for?

& thank ya'll for being patient with me here; a bit new to this type of stuff.
 
My Hamilton is the bronze bushing version as well, I use it frequently.

In this circumstance I wouldn't hesitate to remove both wheels and replace with a pair machined from HDPE/UHMWPE or aluminum maybe even selected & finished wood, using the same snap-ring retention design. As others have mentioned, their function is to set belt tension, change its direction and compensate for changes in the driving/driven belt position- not critical at all. That is, if you have a lathe or access to one; these idlers would make a great learning project. No important dims other than the bearing recess and snap ring groove, just keep making them until you get good ones.

For the bearings I'd go for sealed or shielded. My bronze bushed idlers need a bit of oil every few years.
 
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