Help with faceplate threads

[schemer]

If I understand your post correctly you have a lathe with a 2 1/4-8 threaded spindle nose.
You then turned a 2 1/4-8 plug gauge which works with a new internally threaded part yet not an old internally threaded face plate of the same thread?

Am I on the right track so far?

Yes, sort of. Except my lathe doesn't matter in this case as I am using the faceplate for a welding positioner but bought a 2 1/4 - 8 threaded faceplate and threaded backplate for the project. I bought the faceplate based on size of threads as advertised on ebay in October of 2016 and it has been sitting in a box since so I never had anything to test it with or any reason to doubt the threads. I have taken a few pics but my battery is on the charger at the moment. The two plates (backplate and faceplate) were bought and I just machined the male adapter to screw into them and one works, one does not.

 

[Silverbullet]

One has to be wrong , I'm still thinking the ones a different thread . With threads that large it's hard to think it's the same number and not fitting unless something is wrong on the pitch.

 

[schemer]

One has to be wrong , I'm still thinking the ones a different thread . With threads that large it's hard to think it's the same number and not fitting unless something is wrong on the pitch.

Well one thing for sure is one doesn't work. It will just screw in about 1/8 of a turn so really not even close. Here are some pics of the faceplate with a scale involved and some just to show the thread. They didn't make left handed threads on any of these did they>

 

[Technical Ted]

From the angle of those pictures it sure looks like an 1/8" pitch. That leaves the major diameter. Do you have a way to measure that, like with a pair of old fashion internal calipers or something?

Also, are there any markings on the faceplate? Brand, manufacturer, anything?

From those pictures I wouldn't say those threads look damaged at all. The actually look like they are in very good shape. And they appear to be right hand.

Edit: One more thing... other than pitch and major diameter (pitch diameter really) are they are sharp V thread? For example, Whitworth are rounded and these may be common on lathes from the UK, I really don't know since I have no experience with them. But if it doesn't screw on there certainly is something off.

So, we have correct thread style (thread form), correct pitch and correct pitch diameter. If those three things match up it should screw on.

Ted

 

[Technical Ted]

Sometimes it pays to put some dye, layout blue, Persian blue, Dykem or whatever (even use a black magic marker) on the thread and use this to help determine where the interference is.... this might give a clue.

Ted

 

[schemer]

From the angle of those pictures it sure looks like an 1/8" pitch. That leaves the major diameter. Do you have a way to measure that, like with a pair of old fashion internal calipers or something?

Also, are there any markings on the faceplate? Brand, manufacturer, anything?

From those pictures I wouldn't say those threads look damaged at all. The actually look like they are in very good shape. And they appear to be right hand.

Edit: One more thing... other than pitch and major diameter (pitch diameter really) are they are sharp V thread? For example, Whitworth are rounded and these may be common on lathes from the UK, I really don't know since I have no experience with them. But if it doesn't screw on there certainly is something off.

So, we have correct thread style (thread form), correct pitch and correct pitch diameter. If those three things match up it should screw on.

Ted

I measured the ID on both the one that works and the one that is in the pics, that does not. I used a calipers and they were exact. The faceplate that doesn't work has "flat" threads as opposed to the one that does as it had sharp pointed threads. So I guess the caliper measurement could be off based on that. Maybe the one that works is oversized and has a sloppy thread and throw in my handy work of cutting the threaded adapter, it could all add up. I haven't cut threads in a while and botched the first one as it had rough looking threads and was not symmetrical due to me screwing up somehow. The second one was better but still had rough looking threads but was symmetrical and the "V" shape. But both of my adapters screw into the one backplate just fine although maybe a little sloppy. Maybe my lack of expertise is all that is wrong here but I cut a 0.150 thou relief before cutting the threads and now that I think of it maybe it should have been 0.170 thou? The reason I say that is at the end of the cut where the adapter screwed on the tool was just starting to hit the relief area. My starting major diameter was 4 or 5 thou under 2.250. Anyhow, by the time this is all done, I will persevere.

 

[schemer]

From the angle of those pictures it sure looks like an 1/8" pitch. That leaves the major diameter. Do you have a way to measure that, like with a pair of old fashion internal calipers or something?

Also, are there any markings on the faceplate? Brand, manufacturer, anything?

From those pictures I wouldn't say those threads look damaged at all. The actually look like they are in very good shape. And they appear to be right hand.

Edit: One more thing... other than pitch and major diameter (pitch diameter really) are they are sharp V thread? For example, Whitworth are rounded and these may be common on lathes from the UK, I really don't know since I have no experience with them. But if it doesn't screw on there certainly is something off.

So, we have correct thread style (thread form), correct pitch and correct pitch diameter. If those three things match up it should screw on.

Ted

No brand names or markings. Ebay special with description saying:
2 1/4" x 8 TPI 8 3/8" + dia. Slotted Faceplate for Southbend

 

[schemer]

I used this threading tool to cut the threads:
http://www.ajaxtoolsupply.com/alaxa...MI6PLHvP_P1gIVC6J-Ch2xLwcfEAQYAiABEgLKgvD_BwE

 

[schemer]

Sometimes it pays to put some dye, layout blue, Persian blue, Dykem or whatever (even use a black magic marker) on the thread and use this to help determine where the interference is.... this might give a clue.

Ted

I can surely give that a try but the interference is right away and may just show that. The backplate that I bought new from ebay has pointed sharp threads whereas the faceplate has a flat thread. That seems to be where the problem lies like maybe a different type of thread.

 

[Technical Ted]

I used this threading tool to cut the threads:
http://www.ajaxtoolsupply.com/alaxa...MI6PLHvP_P1gIVC6J-Ch2xLwcfEAQYAiABEgLKgvD_BwE

That's a good ol' 60 degree V thread which is the most common in the USA. I'm more concerned with the thread in the face plate being that same type and at the proper pitch diameter.

Also, another thing to keep in mind, is that face plates can be purchased "blank" meaning no threads to mount on a spindle so the new owner can thread their own as desired. It is certainly possible that the previous owner threaded this himself and didn't take the thread to full depth for some reason... maybe he fitted it to an under size spindle??? Who knows.

If it is the case where the threads just aren't deep enough, it could be put on a lathe, indicated in, and very carefully line up a internal single point threading tool on the original thread and then taken to depth. That is what I would do if I found myself in this situation. It sounds more difficult than it is if you've never done it before. You'd have a nice large bore and coarse thread to give you a big advantage over a much smaller bore. You run the threading tool in using your half nuts, stop the spindle while the tool is inside and then line the tool up in the thread using your compound and cross feed. Do this over and over a few times making very small adjustments until you just start to make a chip and then go from there. Doing this type of work is a great skill to have in your tool belt. Just go very slow and carefully. One additional word of advice is to make sure your threading tool has sufficient clearance because you will be inside a bore and you don't want it rubbing.

Ted