Drill press restoration - Zapins

I started restoring my drill press and need some advice.

I dismantled and cleaned most of it but I am having trouble with one part that probably could do with replacing. The spline shaft has a bent mt3 connector at the end which wobbles by over 5 thousandths. Not a huge issue but if its possible to repair or replace it would be nice to do while I have it all apart. Any ideas on how to replace it or repair? Maybe recut the taper on the lathe?

The shaft dimensions seem to be 12 mm wide, 11.25" long. Also the splines are slightly bent too. They seem to be usable though so not a big deal if I need to reuse.

 

Also any idea how to fix a new set of threads onto the side of the drill press hand crank? The threads are stripped.

 

Helicoils are available at most auto supply places. You'll probably want to get a kit as opposed to individual coils, the kit has an appropriately sized drill bit and tap, several helicoils and an installation tool. Helicoil is a brand name and is the most commonly available brand of thread repair insert but there are others as well such as Timesert.
Threaded inserts such as these are also useful if you have a casting with threaded holes that you expect to use frequently, the inserts are far less likely to strip out with frequent use than a threaded hole in a casting.

 

Perfect. Timeserts look good. The coil ones might come out as I use the handle. I might try rewarding the holes shut and retapping it first but its a weird angle so tapping might be difficult. I haven't decided 100% yet.

I just bought a threading attachment tapper for my lathe. So we will see if that works. Maybe I can rig something to tap the holes straight.

As for the jacobs taper 3 end bit. Maybe I can weld it to replace lost metal and then recut the taper fresh.

What settings do you recommend for tig brazing silicon bronze rod to cast iron? There's a crack that needs fixing. I have heard AC can be used to clean the iron but I've only used DC for bronze to bronze repairs in the past.

 

The coil inserts are very reliable too, and fair bit cheaper. If you're worried about them, a drop or two of red loctite on the outer threads of the insert when you install it and, it's never coming out.

 

Cast Iron repairs are supposed to need preheating of the whole casting before brazing and then slow cooling, so you'd need to get it quite hot before brazing and then bury in sand or if you have a suitable oven/kiln stick it in that for a slow cool down. That drill press is starting to look like a write off in terms of the damage it has suffered, it might be time to put it out to pasture and buy another drill press in better condition.

 

I cut the crack out and brazed in some bronze. Seems to be +/- okish repair? I haven't done a lot of iron brazing but it seems to have mixed iron into the bronze. Unsure whats up with that. I tried brazing on ac mode with 20% cleaning. I zapped the piece until it was hot then fed filler in.

I'm not sure if I can tap through the brazed bit. But I can put another threaded hole farther up the body under the other hole. I think this will work better.

Next is to fix the jt3 spindle. Shouldn't be too hard. Then I'll make new hand holds and paint it all. I'll probably also switch to a synthetic belt instead of the crappy v belt. Seems not to grip very well.

I might also add an LED light or two and do some rewiring.

Yeah its close to a write off but it works pretty well and it cost me $50 like 7 years ago. Also money is a little tight at the moment so another drill, unless it's a cheap one, isn't a super high priority. I might even throw on one of the motors I got from the scrap yard to upgrade the power.

 

Nice work on the brazing, Zap.

You mentioned adding lights. I recently bought a bunch of these and love them. Great mag base, solid flexible neck, bright, convenient switch, and powered by either 240 or 120v AC. Cheap but seem well built.
https://www.amazon.com/gp/product/B07J4ZKGF4/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

I highly recommend them.
Denis

 

Time to make a new splined shaft; that one has been given a hell of a twist somehow and will probably break if you try to drill with it.

If you turn the new shaft in your lathe in 4140, you can get someone with a mill and rotary table with indexing plate, to cut the keyways. Worth doing I think, as the rest of the machine looks to be of good quality.

Another way to weld cast-iron, is to get it just below red-heat in a charcoal hearth; remove it and use cast-iron arc-welding rods to build up the damage; and then return to the heat. As Mark mentioned, a dry-sand burial works well, or just bury it in charcoal and turn the blower off and allow it to cool slowly. I did this when I broke two mounting flanges off my PTO belt drive on the tractor, worked out well,

Restoring workshop machines is fun,

Cheers Charlie

 

Hmm. I'd love to make another shaft. I'm not sure if my lathe can cut to the right accuracy for it. But maybe I'll try make one out of mild steel and see if I can get the dimensions close then try it out of 4140.

There is a machine shop near me that can probably cut the splines in. Not sure what they'd charge for that but it might be worth a try.

I might swing by there tomorrow morning and see if they can just make the entire new part for me to spec. That way I won't have to worry about getting the dimensions exact. If its 40 to 60 bucks to make a new one then it might be worth it. Especially if they do a jacobs taper on the end.

Or maybe I should just say to hell with it and make it all myself lol. It would certainly level up my machining skills.

I need to level the tailstock and bed first somehow but I don't really have the right equipment to do it. So we will see.

Thanks on the brazing. I'm still not sure I did it right I think I somehow overheated the iron and bits melted into the bronze because there are islands of iron inside the bronze somehow. I always feel like I'm flying be the seat of my pants brazing iron. Its a pretty awful feeling. I think there are some small inclusions and maybe pockets of crap in the weld along the edges where the bronze meets the iron leading to the small pockets on the surface. I'd hit it again with the tig torch to fix them but I'm afraid I'd get a crack or something. I can always fill it in with paint especially since I think the brazed joint is strong enough to hold the load it will be under.

 

If you make a new shaft with spline, I would stronly suggest using 4140 Prehard. It is about Rc 28 to 32 machines very nicely. It is hard enough to give good service as machined and would resist twist better than annealed steel. I heat treat annealed 4140 that I occasioanlly buy on eBay. I convert it to PH. Not at all hard to do. The annealed material seems to show up on eBay more and is usually less money than PH.

I think 60 dollars for machining that part would be a heck of a bargain. Cutting the taper on the lathe should not be hard to do. I've done a good number. Perfection is not required and I know a few ways to make it easier to get a very good result. Also cutting the spline with a mill would not be real hard to do. If you have an indexer or rotary table, you'd need to make a cutter from HSS---very doable with some patience. Could be single tooth like a gear hob fly cutter.

All this is quite easyu for me to say from my easy chair, of course.

Denis

 

I see similar shafts are $400-$500 USD as a spare part.

 

Jeeze 500 bucks would buy me a new top end drill press haha.

Whats the difference between prehard and annealed? Can I buy from ebay and make a shaft or no?

I think the shaft is made from soft mild steel. It files very easily.

I spent hours fine tuning my tailstock. I think its within 2 thou of true over about 14". Which i feel like isn't good enough so I bought a tail stock alignment bar to get it closer. I had to shim my tailstock by 11 thousandths. Crazy. The damn thing must have a ton of wear on it to be so far off. But we will see once the alignment bar arrives. Also but some other tooling like a carbide threader digital calipers and 1,2,3 block.

 

You sure the lathe is sitting perfectly level?

 

Zapins, It is not impossible that your tailstock could have a lot of wear. Determining sources of inaccuracy in a lathe and correcting them can be quite involved. The key question is how accurate does it REALLY need to be over 14", say. To make the part in question you need to accurately turn a short taper and somewhat accurately turn maybe 5 inches to be cut into a spline. You could easily spend a couple months tweaking your lathe. I would suggest you not go that direction until or unless it is actually lathe inaccuracy that limits your success in making parts. The fabrication shop where I occasionally hang out tmakes parts all day long and makes money at it is using 3 fairly worn lathes. The owner is well aware of the wear, but he and his workers have simply learned how to compensate for it. They feel they don't have the time to stop, tear down a machine, and make it "accurate" again. But they make very good parts and make good money doing it.

If you want to get into it, there are numerous books available. Also there are several forums where you could ask questions of folks who have likely dealt with your specific lathe. The first one I would recommend for you is Home Shop Machinist. There you would find maybe hundreds of prior threads on lathe restoration in their archives. Also, some pretty expert folks hang out there. I would think you might want to spend some time there. Looking at the question piecemeal here could be done. But this site really seems best suited and strongest in the casting realm and HSM and PracticalMachinist are strong in machine restoration, maintenance, and use.

You can buy 4140 prehard from a lot of sources. The easiest one and a good supplier in general is McMaster Carr. Here is a copy of their page that did not format well here:

High-Strength Multipurpose 4140 Alloy Steel Rods

• Yield Strength: 130,000 psi
• Hardness: Rockwell C32 (Hard)
• Specifications Met: ASTM A108

Often called ETD-150, these rods are made from a modified version of 4140 alloy steel and have been drawn at high temperatures for excellent strength. Also known as chrome-moly steel, they are used for a wide range of parts, such as gears, axles, shafts, collets, and die holders. They resist fracturing from repeated stress.

For technical drawings and 3-D models, click on a part number.

Certificates with a traceable lot number are available for these products. Download certificates from ACTIVITY after your order ships.


Dia. Dia. Tolerance Heat
Treatment Straightness
Tolerance 1/2 ft.
Lg. 1 ft.
Lg. 2 ft.
Lg. 3 ft.
Lg. 6 ft.
Lg. 12 ft.
Lg.
1" -0.006" to 0" Hardened 3/16" per 10 ft. 6818T25
$16.60
$26.75
$42.43
$53.49
$92.23
$147.57

Denis

 

Yeah tuning the lathe back to good condition would involve rescraping or grinding the ways which would cost big bucks. I might as well buy a better lathe at that point but he tailstock alignment is pretty annoying when it isn't running true. It gives me tapers on everything I make which makes it next to impossible to do nice work. So at least that is a minimum issue I need to fix. But I agree I'll try not to go too nuts fixing it up haha. It seems to be a bit of a rabbit hole for sure.

I took the spindle to the machine shop but they don't have an indexing head to cut the splines so I'm out of luck locally at that shop. I guess I might be able to cut my own splines by "keying" them in on the lathe but this might be a rough process. What do you think? Could I do that with prehardened 4140 with hss bits?

I tried to hammer the shaft straight and messed it up more. Sigh.

If I have to make a new shaft I wonder if I shouldn't just install larger ID bearings say 20 mm instead of 12 mm and have a beefier larger shaft that won't be as likely to bend out of round. Or heck one that has a removable taper on the end. I don't see any reason I couldn't upside the shaft if I have to make a new one.

 

I'd be inclined to get the shaft as straight as possible and then use a small cheap plunge router mounted in the lathe toolpost (as a cheap toolpost grinder) with a small pink ruby grinding wheel (lasts longer with little change to the wheel diameter) to touch up the nose taper.

This video covers some checking of a similar vertical mill spindle:

 

While I think about it, if you assembled the drill shaft into the housing with the bearings and then made a jig to sit it over the lathe with the spline end driven by the lathe chuck, the nose taper could be ground in situ which would cancel any shaft wobbles it may have....just never pull the assembly apart again without marking where each inner race in on the shaft and each outer race is on the tube/housing.