Broken threads on the QCTP of my compound slide

Even my little 7x12 uses an M10 bolt for the toolpost mount. If you've got a drill press you should be good to go (assuming you've got the right drill and an M10 tap). You can chuck a smaller but close-fitting drill in the drill press to align the top slide -- drop the chucked-up drill in the hole. Once aligned clamp it down, switch to the drill you need for your M10 threaded hole and go for it.

Feed slow when enlarging a hole drilled in cast iron. It tends to pull drills into pre-drilled holes. Also, you need to keep in mind that you can get both M10-1 and M10-1.5 bolts. They will require slightly different-sized holes for tapping.
 
homebrewed said:
Even my little 7x12 uses an M10 bolt for the toolpost mount. If you've got a drill press you should be good to go (assuming you've got the right drill and an M10 tap). You can chuck a smaller but close-fitting drill in the drill press to align the top slide -- drop the chucked-up drill in the hole. Once aligned clamp it down, switch to the drill you need for your M10 threaded hole and go for it.

Feed slow when enlarging a hole drilled in cast iron. It tends to pull drills into pre-drilled holes. Also, you need to keep in mind that you can get both M10-1 and M10-1.5 bolts. They will require slightly different-sized holes for tapping.
Click to expand...
Before you start enlarging holes: one potential issue is the mounting hole in your QCTP. You might need to either drill that out (if that's possible) or make/buy something that's compatible with the size of bolt or stud you use......
 
ttabbal said:
If you have a mill, it would help make sure you drill/tap straight. Or a drill press? I would remove the top of the compound to do the job so you don't get chips in the sliding surfaces. My compound (PM1127) came with an M10 hold down. I wouldn't want to go smaller than that. I made a new stud as well, that has a wider section in the middle. So it can tighten against the compound top to ensure everything is good before installing the QCTP. For now, just use a bolt or bit of all-thread to hold the QCTP so you can make a new stud or whatever as needed.
Click to expand...
This is the way I would do it. In fact, I did a similar job by buying a used (but good) tap. Be really careful. You will only get one chance. Not really...if you mess up, you can do the compound replacement with a solid block trick. That will work in case you goof up. I would not attack it with a welder, even though I know how to weld cast iron. Wrong application of a tool.
 
Ok - was able to reasonably stabilize my current tool post last night. I mounted the current stud in the lathe chuck and proceeded to cut fresh threads on one end of it on the unthreaded part - then I just cut off about 1/4'' off the end. It found new 'meat' and I was able to at least temporarily secure my QCTP in place to make the new stud.

So, currently, I have a 9/16'' 18tpi hole that I want to rethread to 5/8'' 18tpi. I have a 5/8'' steel rod that I'd like to use to make the new stud. Was looking at the machinists charts trying to determine the proper OD of the rod for external threading. Found this:

ANSI External Screw Threads Size Tolerances Chart

ANSI/ ASME EXTERNAL Screw Thread Size Chart. All units are in inches. Unified Screw Threads per. ANSI/ASME B1.1-1989 (R2001), R2001) Nomenclature, are used. Acceptability criteria are described in ANSI/ASME B1.3M-1992 (R2001).
www.engineersedge.com

1651595218980.png


What should I turn the OD of that 5/8'' rod down to to properly thread it to 5/8'' 18 tpi?
 
homebrewed said:
Before you start enlarging holes: one potential issue is the mounting hole in your QCTP. You might need to either drill that out (if that's possible) or make/buy something that's compatible with the size of bolt or stud you use......
Click to expand...
Understand - I plan on enlarging the hole to 5/8'' ID and threading the bottom of the new stud to fit that, and then turning down the body of the stud to fit the 9/16'' +/- hole in my QCTP... Just hope this rookie is up to this task.
 
You want OD to be in the range of major diameter. Ideally, you then measure pitch diameter with a thread mic, thread wires, or other devices. You can also try to thread the mating part on it to match. Just grabbing a nut could throw it off if the tolerance stacks incorrectly. So it might fit the nut, but not the mating part. Just something to be aware of.
 
I just have the basic HSS threading set - I don't have any thread mic. What I'm really looking to know with this 5/8'' rod is: do I run the 5/8 die on it as is or should I turn it down to say .6230 or .6240... etc
 
Thread wires are cheap. You can use a mic or even a caliper to measure them. But this is a one time thing really. So if you don't want to get them, get as close as you can.

When you say HSS threading set... Tap/die set? They should cut close enough. I thought you were going to single point the threads as you were using a lathe, but a die would work. It might be tough to run on, most of the sets you get locally are really intended for repair not cutting new threads. They can do it though. Or get close with single point and run the repair die over it.
 
ttabbal said:
Thread wires are cheap. You can use a mic or even a caliper to measure them. But this is a one time thing really. So if you don't want to get them, get as close as you can.

When you say HSS threading set... Tap/die set? They should cut close enough. I thought you were going to single point the threads as you were using a lathe, but a die would work. It might be tough to run on, most of the sets you get locally are really intended for repair not cutting new threads. They can do it though. Or get close with single point and run the repair die over it.
Click to expand...
I am not capable of running single point threading.... My threading dies are all I have at this point.
 
You must log in or register to reply here.
Back
Top