camel back drill press

[Joe Michaels]

Hello Todd:

I am glad you enjoyed our phone visit. I do tend to ramble on !

I will try to address your questions as best I can:
Regarding the fit of the quill in the bored/semi-split casting-
Anytime you rebore something like that casting, the risk is losing the original centerline. When a bushing or sleeve is added to restore things to the original fit,
this adds two diameters which must be concentric. Anytime parts are assembled or stacked together, there is some risk of introducing inaccuracy relative to the original reference line or surface. On something like your old drill, it a few thousandths one way or another would not make much, if any, difference in the overall machine tool.

Boring a semi-split housing is trickier due to the splits, as well as the fact that neither bore mat be round or a true cylinder (possible tapered wear). Assuming the part could be setup for boring, the next question is how much iron would be left if about 1/8" (min) or 3/16" (preferable) per side were bored out ? Assuming that enough iron remained for this boring out, we then ask ourselves what the sleeve should be made from. If the sleeve were made of steel, it would be harder than the original
iron, and might cause wear on the quill's sliding surfaces. For a drill press seeing occasional use, making the sleeve from something like A=36 hot rolled bar would be OK. I'd make the sleeve with a flange or collar on the top. This would keep the sleeve from sliding out of the bored fit in the arm. This flanged end would also help strengthen the sleeve. Another choice for sleeve material would be 'drawn over mandrel' (known as DOM) steel tube, machined to final size & with enough wall to allow for a collar or flange on the top end. The flange need not be any much bigger in diameter than the diameter of the sleeve fitted into the bored hole.

To hold the sleeve in place, I'd drill and tap thru the casting and into the sleeve for a few setscrews. These would function as dowels to keep the sleeve from sliding
within the bored fit in the casting. I'd slit the sleeve full length vs the original configuration on the casting. Don't ask me why, just gut sense.

My own recommendation here is to leave well enough alone with the fit of the quill in the bore of the arm. Hard chroming the quill only improves or increases the OD of the quill. It still leaves the bored fit in the casting to be addressed. It comes down to how much money you want to sink into this drill press and what the end result will be. A worn camelback drill will never be a toolroom machine tool. Live with what's there as far as the quill and its fit in the bore of the casting. For drilling holes in work like structural steel, farm implement parts or trailer hitch parts, the drill will be just fine.

OK, moving onto your question about the broken gear tooth- Much has been written on this 'board about repairing broken teeth on spur gears. Slow speed open gearing is fairly tolerant of repairs. One old tried and true repair is dress off the broken tooth at its root in the rim of the gear. A row of holes is then drilled along the centerline of the broken tooth, and these holes are tapped. Diameter of the holes/tappings should be slightly larger than the thickness of the tooth at its widest (see the Machinery's Handbook for basic spur gear design formulas). Studs made from steel rod such as drill rod work well for this fix. When the screws (or studs) are run in hard, they should form a row across where the tooth used to be. Using files, the shanks of these studs are then filed to the profile of the gear teeth.

Method 2: if you have access to an oxyacetylene torch, the broken tooth can be repaired using bronze brazing. Depending on tooth size, you can simply build up the area of the broken tooth with bronze brazing and file to get the profile of the tooth. If a larger tooth, follow the above method to get some studs tapped into the rim of the gear, then build up with brazing to incorporate the studs. File the tooth to final profile.

The beauty of a brazed repair is that if the tooth is slightly larger or off a little in its profile, as the gearing turns, the repair will 'run in'. The bronze is somewhat ductile, and as the gearing turns, the original teeth on the mating gear will cold-work the bronze repaired tooth to form it to profile. This cold working work-hardens the bronze and burnishes it to a good surface finish. A cautionary note here: the brazed repair must be quite close in profile to the original teeth for this cold-working to happen.
If the brazed tooth is not dressed very close to original profile, you could wind up either binding the gearing or breaking other teeth. Rolling the gearing with some bluing as you get close with filing the brazed repair to profile and feeling and seeing how the repair meshes are the way to go about it. The beauty of a brazed repair is that if you mess up and take off too much during the dressing of the tooth, you can lay more brazing on and try again.

Brazing is a great process, often overlooked in today's world as people tend to think in terms of MIG or TIG welding. For work on old machinery, having the capability and skill to braze is a vital thing in my opinion.

Best regards-
Joe Michaels

 

[todda323]

Thanks Joe. Always great advice. By the way I look forward to our next conversation. I was telling the wife we may need to take a vacation up north some time as I was briefing her about some of the stories you told me. She was afraid she'd never get me home. As it stands I can't go into Lowes without seeing someone I know and investing in a hour of conversation. She has learned that when I get to talking she just heads for the garden section.

I was reading about .020 run out at the quill. If in the big scheme of things this is irrelevant because this is not a precision machine and would be used for exactly what you described then sleeping dogs will rest. I do tend to make mountains out of mole hills.

As for the gear I will see about having it repaired in the future as I do not have a lathe nor a mill. Just Dave suggested buying one. I'm not sure how this would compare to having it repaired cost wise. Additionally I will reference some of the folks I know that are machinists locally to get their input. Looking at the gear closely it looks like there is a difference in the metal. I wonder if it has already been repaired once. I know certain specialist places will re make gears if you send them out. I would guess the gear in question to be cast iron. Please correct me if I'm wrong. I'm taking in to consideration all you have to go by is a visual observation. As well I would guess I would, similarly, want a gear of cast iron if I purchased one or had one made so as to not run steel against cast under stress loads.

 

[dundeeshopnut]

No lathe or mill needed to braze in a tooth or 2 Small angle grinder or die grinder is the only power tool you will want and even they can be substituted for a hack saw.

 

[Joe Michaels]

Hello Todd:

I would not throw money into having a new gear made, nor into doing a 'machine shop' type repair of the damaged/broken tooth/teeth. As I wrote, plenty of cast iron gears in such applications as lathe back gearing and other open gearing have been repaired using tapped-in studs and/or brazing. No machine tools other than maybe drilling the holes in the rim of the gear for tapping and setting the studs. Otherwise, it is a job of using one's eye and hand filing to form the repair tooth profile. Plenty of lathe back gears are running teeth repaired with steel studs tapped into the cast iron rim of the gear and filed to form the teeth. You could use Grade 8 bolts with un= threaded shanks. Check the depth of the tapped holes in the rim and cut the threaded ends of the bolts so they bottom in the tappings and leave very little thread exposed. Run in a bolt as tight as you can get it, cut off its head and run in its neighbor, repeating the process until you have a chain of bolt shanks very nearly touching each other. File off the outer ends to match the circumference of the gear, then start filing the tooth profile. A knife edge file and some patience, a good eye, and skill with the files are about it.

Learning to file was something taught to us back in the mid 1960's and something a machinist was expected to know how to do. This is oldtime machinist's or mechanic's work. I was in an old junkyard a few years back and saw the remains of a the winches and booms from an old tow truck. It had hand operated winches to raise and lower the booms, with open gearing. I remember seeing a few teeth on the open winch gearing had been repaired with tapped-in studs filed to profile.

If a person did not 'come up' in the times of my generation, nor worked in backwoods places or overseas, it puts them in a certain mindset. That is the mindset of having to rely on software, or being able to buy replacement parts rather than make or repair what's there, or expecting to have work done on machine tools. When you work in backwoods places where people are short on cash and a long ways from the nearest supply house, or when you work overseas and the nearest paved road is 100 miles away and there were no cell phones nor computers, you develop a different mindset. You rely on your basic skills and imagination and work with whomever and whatever is at hand to make a job happen. It is easy to scroll down on a website for something like Boston Gear, Martin Gear, McMaster-Carr, etc and find a stock gear (and then discover it costs a young fortune or has considerable lead time from date of order). It is easy to think in terms of sending work to machine shops with the capabilities to cut new gears or do hard chrome buildup and precision grinding... until the shop says this is a job that they'd rather not handle, or tells you their hourly rate + materials... Hence, when working to set something like a camelback drill that was rode hard and put up wet to rights, thinking like an oldtime backwoods mechanic is a good starting point. It will avoid running up heavy expenses and get your drill press working well enough for what you are likely to be doing with it. It will also develop your own skills and how you approach a job without benefit of manuals or software.