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Asking for Some Advice/Help SB Heavy 10 Threading

mitchapalooza88

Plastic
Joined
Apr 17, 2018
Hello all,
I have probably tried this about 15 times and never gotten a single point thread to work. I am starting to wonder if my lathe might have metric gears because the thread will always start but then it binds like its slightly the wrong TPI.

I'm still learning the ropes here but I have watched just about every you tube tutorial on the web and from an operational stand point I think I am doing it right.

My last thread I tried is a 2 1/4-8 and sure enough it bound up.

IMG_0762.jpg
 
can you verify the pitch using a pitch gauge? If not, a dial indicator should tell you if the spindle rotates in one inch of carriage movement. Or some plasticine/ playdoh and a ruler.

If the pitch is correct, what are you using to determine fit? Is it a spindle nose protector? If you're making stuff for your spindle, then making a go-gage using thread wires will make your life alot easier, rather than having to take the chuck off, turn it around and see if the threaded piece you're making threads on. My guess is that the pitch is correct but the threads have not been cut deep enough.
 
I would verify the pitch with a pitch gauge if you have one. Dial indicator to measure travel per revolution as mentioned above. Or scratch a standard pitch and compare it to a bolt you have.

If the pitch is wrong I would read through this thread about a flipped gear on the leadscrew. It is for a 9A so I am not sure you can do the same thing on a heavy 10 but worth checking.

Strange threading problem

I am not sure what threading bar you are using for the 2 1/4 8 internal thread but if it’s the carbide insert type, it might not have the clearance for that course a thread. I have one that looks like it will work but will thread the first thread perfectly and then rub just enough to not cut the rest of the threads deep enough. Worth checking as well.

Hope this helps.

Ben
 
Binding can come from incorrect pitch, but it can also come from the threadform itself (wrong angle, wrong depth, incorrect crest or root, etc.). Of course it is hard to know without measurements, but your threads in that picture look really shallow to me.

allan
 
how do you have your compound set ? i may be wrong but our instructor showed us outside thread compound to the left inside tread compound to the right and 29-1/2 deg. but with out a optical competitor its all cut and try or hammer to fit file to finish
 
I would work out your issues on an external thread first before adding the factors outlined above in other replies.

also, tell us which generation of 10L you have and its condition. they made a few version of the heavy 10, so it could be one of a number of different animals you are working on.

just a few things that also come to mind, are you taking up the backlash before actually cutting the thread? does your lathe have a taper attachment, and is it disengaged so it doesn't cut a taper unintentionally? had that happen to me, if cutting a straight diameter it would have been obvious, but being it happed when threading, it really had me baffled for a bit!
 
I think my problem is the threads aren't deep enough. Which would make sense, I don't think my process is correct using Machinist Handbook numbers.

2 1/4 -8 Specs for internal thread 3B are;

Minor Dia
2.1150-2.1297

Pitch Diameter
2.1688-2.1766

Major Diameter
2.2500

1. I set my Compound slide to its full extent toward the cut
2. I bored the hole to the Minor Dia. I hit 2.12.
2. Then I zeroed the cross slide.
3. Then I figured (Major-Minor)/2 or (2.25-2.12)/2 = .065 was how much I had to cut with the cross slide.

I think that is wrong though because the tip of the cutting tool is a point not a flat? How do I calculate the right depth of cut from the handbook?
 
I think my problem is the threads aren't deep enough. Which would make sense, I don't think my process is correct using Machinist Handbook numbers.

2 1/4 -8 Specs for internal thread 3B are;

Minor Dia
2.1150-2.1297

Pitch Diameter
2.1688-2.1766

Major Diameter
2.2500

1. I set my Compound slide to its full extent toward the cut
2. I bored the hole to the Minor Dia. I hit 2.12.
2. Then I zeroed the cross slide.
3. Then I figured (Major-Minor)/2 or (2.25-2.12)/2 = .065 was how much I had to cut with the cross slide.

I think that is wrong though because the tip of the cutting tool is a point not a flat? How do I calculate the right depth of cut from the handbook?


I have only cut a couple inside diameter threads and I was lucky to have an external thread to use as a go no-go gauge. Maybe cut an outside diameter thread first on something and use it as a gauge so you don't change your lead screw engagement positions on the half nut?
 
What do you mean by "it bound up"?

How are you testing your cut thread pitch?

What exactly are you trying to cut? A backplate? A spindle nose protector?

What makes you think that you might be cutting a metric thread?

Show PICTURES of your lathe, gearing and setup.

Kevin has a good suggestion on making yourself a GO-GAGE for your project. Cutting an outside thread is much easier than cutting an inside. In fact, having the GO-GAGE is about the only way a hobbiest can test an inside thread for the proper fit.
 
I set my Compound slide to its full extent toward the cut
I'm not sure what you mean by this - the handle on the compound should be pointing at about 7:30 on the clock - 29 degrees off 6 o'clock.

I think that is wrong though because the tip of the cutting tool is a point not a flat? How do I calculate the right depth of cut from the handbook?

I think you are on the right track here. Sharp V threads and Unified National threads don't get along.
What I did, and others have done, it to create a dummy spindle nose with the correct pitch diameter - that's the important bit. You measure over wires set in the threads to verify pitch diameter. Here's a resource that will do that calculation for you:

UN imperial screw thread calculator

It also gives wire sizes, but you can adjust the wire size and get the new target over-wires dimension. SO you could just use say shanks of 3 close to correct drill bits if you don't have a set of thread wires. I've used MIG wire and brazing rod in a pinch, just measure the diameter of the thing you are using that is close to the right dimension, and enter that in the calculator.

So you use this info to make a dummy spindle with the correct 2A thread, which you can then use to gauge your internal thread, which is impossible to measure over wires. Get close, then tiny shaves till your dummy spindle fits.

You can, with a little fiddling, pick up existing threads and cut them deeper.
To do this, set up the lathe for the proper thread pitch. Let the lathe move the carriage towards the work to get all the slack out. You want to be close to but not cutting the ID of the hole. Get in the hole a thread or two.
Now, loosening the boring bar in the holder, and backing your compound out, make your cutter fit down into the existing partially cut thread. Tighten up your boring bar holder, and hand turn the chuck a little to make sure you are right. You should now be "back in the groove" and ready to deepen those existing threads.
 
Lots of good stuff from others but I'd like to offer up a few more tidbits for internal threading. I set the compound opposite from where it would be for external threading (29.5° on the other side of center, see photo). It can be a bit awkward to manipulate the compound in that configuration, but it give better results like it does for external threads. At 29.5°, you take the cosine of that angle and divide the expected depth by that, so cosine of 29.5° is 0.87 so for a thread depth (from theoreticalmachinist.com for 2.25 x 8tpi 2B) of 0.055 (minimum for class 2B), 0.055/0.087 = 0.063, so the compound dial would move 0.063.

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Not having the proper tools to measure thread sizing I did this on a part that I had to single point. It was rather time consuming but it worked well.

I needed to duplicate a part that had a 1.5 inch internal thread. I made a male threaded part in the lathe out of some steel scrap mystery alloy and cut the threads until the fit in the existing part was perfect. So I created my go nogo gauge you could say.

I then made my female threaded part and did test fittings with my newly made gauge until it had the same decent fit.
Crude and time consuming but it worked well.
 
Crude and time consuming but it worked well.

Yes, but this is about the only way to do it to get a proper fit. There isn't an inside thread micrometer and you can't use wires to measure your pitch diameter.

If you really need an internal thread to be a particular fit, you could purchase the correct fit tap and use it to cut the last 0.005-0.010" to finish it off.
 
I think my problem is the threads aren't deep enough. Which would make sense, I don't think my process is correct using Machinist Handbook numbers.

2 1/4 -8 Specs for internal thread 3B are;

Minor Dia
2.1150-2.1297

Pitch Diameter
2.1688-2.1766

Major Diameter
2.2500

1. I set my Compound slide to its full extent toward the cut
2. I bored the hole to the Minor Dia. I hit 2.12.
2. Then I zeroed the cross slide.
3. Then I figured (Major-Minor)/2 or (2.25-2.12)/2 = .065 was how much I had to cut with the cross slide.

I think that is wrong though because the tip of the cutting tool is a point not a flat? How do I calculate the right depth of cut from the handbook?

If your tool is sharp-pointed and you cut to numbers meant for a tip with a flat, then your thread is going to come out shallow. You'll need to keep cutting to the whole depth of a sharp-pointed tool. Making a dummy spindle is a good idea. Get your over-wires measurement and just keep threading until you duplicate that, then you know that your gauge is going to be effective when you cut your internal thread.
 
Not having the proper tools to measure thread sizing I did this on a part that I had to single point. It was rather time consuming but it worked well.

I needed to duplicate a part that had a 1.5 inch internal thread. I made a male threaded part in the lathe out of some steel scrap mystery alloy and cut the threads until the fit in the existing part was perfect. So I created my go nogo gauge you could say.

I then made my female threaded part and did test fittings with my newly made gauge until it had the same decent fit.
Crude and time consuming but it worked well.

If you do many, you'll end up with a metric shit-ton of them.

ACtC-3cTMbmDCERrM0y-UPSVrZfBqm0BpK0odBg0sWFHUIvoWmqwhwd6Ge9PbOJ_utvlOjG3f_qD9zHKcHL-6sL-xwYFJja7jHVv6fUcxX4wF3Q1GEbWOVMGhducK__zc-gahOoTLNjr2nO4pUeEyDukabowpw=w1202-h889-no
 
Interestingly, you can do this mostly by eye. Look at the bore and threads on one of your existing backplates. Make your replacement look just like it. The roots of the threads should look the same, if the minor diameter is the same.

allan
 
I really appreciate all the advice from everyone. Thats what makes this place great.

I don't currently own a set of thread wires. So that's a good call and I will pick up a set. Thats one thing about learning to machine, instead of just blindly going out and buying stuff. I am trying to do new projects and acquire new gear as it is needed. Sometimes what you don't know, well you don't know. Its great to get some tips.

And I did not make a go-gage, but that is a great idea. This project is for a back plate for my 4-jaw chuck and having a go-gage would probably be used again in the future. Also I quickly realized during this project that there is no good way to measure major dia on an internal thread.

So I was able to get back into the thread and cut it deeper. I am positive that my calculations for thread depth are wrong because I am using a sharp point tip. After cutting the thread deeper, I was able to get the backplate to get on the spindle. And I finished up the part.
 
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