Advice (for novice) building 1st 1957 southbend backplate!! Thanks!

Homebrewblob · Aug 21, 2020

I’m planing to build a new threaded back plate for my SB16/threaded nose and I have no idea where to start.

So far I have Sourced (not Purchased) a 2” x 10” round steel blank from my local metal Supermarket and it’s mild steel. (No hole in center!)

My questions for the SB gods on here is

1 is 2x10 big enough for a 10 inch 4 jaw chuck and to cover the length of threads correctly?

2 is mild steel suitable for this application? (What about spicy steel? Lol (jokes!))

3 I have a simple indexable threading tool (I have NO HHS) will this work or do I need a Specific threading geometry?

4 any tips GREATLY appreciated

5 anything I forgot or overlooked

6 is my threaded nose 2-3/8 x 6tpi?? I get conflicting info and I’m terrible at identifying threads, any one wanna offer advice I will greatly appreciate it!

texasgeartrain · Aug 21, 2020

Homebrewblob said:
6 is my threaded nose 2-3/8 x 6tpi?? I get conflicting info and I’m terrible at identifying threads, any one wanna offer advice I will greatly appreciate it!

Yes, 16's are 2 3/8". To check: Set digital calipers to 1". Set two point of calipers in two thread lower cuts. Count the number of high portion of threads, inside of the two point of calipers.

OD, measure od with calipers. Convert to faction, use google or chart.

texasgeartrain · Aug 21, 2020

10" OD is likely more than big enough. but to answer question, what is the distance between mounting bolts holes, for chuck to back plate.

Not sure on the 2" thick part, need to measure from end of threads to shoulder that backplates stop on.

Probably want a more experienced guy than me, on tricks for cutting internal threads. Or use a really big tap !

Homebrewblob · Aug 21, 2020

texasgunsmith said:
Yes, 16's are 2 3/8". To check: Set digital calipers to 1". Set two point of calipers in two thread lower cuts. Count the number of high portion of threads, inside of the two point of calipers.

View attachment 297399

OD, measure od with calipers. Convert to faction, use google or chart.

Thanks big Tex, looks like according to your advice it is in fact 2-3/8 x 6 appreciate your time brother

Homebrewblob · Aug 21, 2020

Measuring the Od of the shaft

Measuring from the valleys of the threads

Err vice versa sorry

dalmatiangirl61 · Aug 21, 2020

Have you looked at just buying a cast iron blank but prethreaded backing plate, Enco used to carry them, wag is that MSC has them.

Homebrewblob · Aug 21, 2020

dalmatiangirl61 said:
Have you looked at just buying a cast iron blank but prethreaded backing plate, Enco used to carry them, wag is that MSC has them.

I have, the prices are pretty high (as expected for a semi machined Precision part) and I can get the “blank” for half the price (also I kinda want to try ya know?)

SBLatheman · Aug 21, 2020

Steel is a poor choice for a threaded chuck back. It will tend to gaul and get stuck.
Cast iron would be a better choice.
Does your 4-jaw require a 10” diameter back? Most of them don’t(independent chuck jaws). Details of the back side of the chuck would help.
Ted

Homebrewblob · Aug 21, 2020

I’m not sure how to mount the blank in my 9” 6 jaw atm

dalmatiangirl61 · Aug 21, 2020

Homebrewblob said:
I have, the prices are pretty high (as expected for a semi machined Precision part) and I can get the “blank” for half the price (also I kinda want to try ya know?)

I just looked it up, holy cow, they got expensive! Don't remember them being anywhere near that expensive, but its been awhile....

Homebrewblob · Aug 21, 2020

SBLatheman said:
Steel is a poor choice for a threaded chuck back. It will tend to gaul and get stuck.
Cast iron would be a better choice.
Does your 4-jaw require a 10” diameter back? Most of them don’t(independent chuck jaws). Details of the back side of the chuck would help.
Ted

The chuck I’m thinking of using is the G9867 from grizzly, I talked to tech and they said it’s not a solid chuck (4 voids in back on perimeter) and it’s a “plain back” that was all they could tell me. So at the current time I’m waiting to receive that chuck to really get a good understanding of the back, it has 4 through Allen screws in the face.
If it’s not good (I know a solid chuck is better!!) I’ll send it back. I’m pretty much just trying the get the backplate semi complete pending whatever chuck I decide to use.
I would like to get started on the backplate and get it mounted if possible first and then fit it to a chuck.

Or am I putting the wagon before the horse?

SBLatheman · Aug 21, 2020

Homebrewblob said:
The chuck I’m thinking of using is the G9867 from grizzly, I talked to tech and they said it’s not a solid chuck (4 voids in back on perimeter) and it’s a “plain back” that was all they could tell me. So at the current time I’m waiting to receive that chuck to really get a good understanding of the back, it has 4 through Allen screws in the face.
If it’s not good (I know a solid chuck is better!!) I’ll send it back. I’m pretty much just trying the get the backplate semi complete pending whatever chuck I decide to use.
I would like to get started on the backplate and get it mounted if possible first and then fit it to a chuck.

Or am I putting the wagon before the horse?

If you make a 10” back when it only needs a 6”... :nutter:

Homebrewblob · Aug 21, 2020

SBLatheman said:
If you make a 10” back when it only needs a 6”...

Haha, yeah that’s why I asked.
I imagine I’m not the first guy to have to cut 4 inches off the diameter of the work.
I went with 10 because my 9” 6 jaw has a 9” backplate.

And anyway I figured at worst I’d have a nice plate to make a dog drive plate out of

Homebrewblob · Aug 21, 2020

dalmatiangirl61 said:
I just looked it up, holy cow, they got expensive! Don't remember them being anywhere near that expensive, but its been awhile....

Yeah that was my first thought was to just buy one.

But then I seen the prices and figured why not just make one after all I see that said on here a lot

johnoder · Aug 21, 2020

But then I seen the prices

Get familiar with measuring threads - like the three wire method

Measure and document your spindle nose

Make a "plug" gage exactly like the spindle nose

Now you have the wherewithal to make a back plate that actually fits your spindle

With care, you could use such a gage to enable making a number of back plates- whenever needed

Homebrewblob · Aug 21, 2020

johnoder said:
Get familiar with measuring threads - like the three wire method

Measure and document your spindle nose

Make a "plug" gage exactly like the spindle nose

Now you have the wherewithal to make a back plate that actually fits your spindle

With care, you could use such a gage to enable making a number of back plates- whenever needed

Making a gauge is a good idea, what’s the benefit to just using my spindle as a gauge ( givin I use common sense and don’t force a part onto my spindle?)?

Rudd · Aug 21, 2020

Listen to John's advice. I have done it both ways on a 13. Think it through - you cut some threads, you need to see if it fits. How are you going to do that and not loose angular register - i.e, hit the thread in the same place after testing? You take the chuck w/ backplate in it off, turn it around, and try to thread that heavy monster one. It is no fun.
Make the test spindle nose, no removing the chuck, just try it. And when you are done, put it away for the next time you want to make a backplate, or driver plate, or faceplate.
Measuring over wires is really pretty easy. If you have some wire that is close to the recommended .0962" diameter they will work for your purpose. 3/32 drill rod (.09375") would be close enough I think, but I'm open to correction.

Homebrewblob · Aug 21, 2020

Rudd said:
Listen to John's advice. I have done it both ways on a 13. Think it through - you cut some threads, you need to see if it fits. How are you going to do that and not loose angular register - i.e, hit the thread in the same place after testing? You take the chuck w/ backplate in it off, turn it around, and try to thread that heavy monster one. It is no fun.
Make the test spindle nose, no removing the chuck, just try it. And when you are done, put it away for the next time you want to make a backplate, or driver plate, or faceplate.
Measuring over wires is really pretty easy. If you have some wire that is close to the recommended .0962" diameter they will work for your purpose. 3/32 drill rod (.09375") would be close enough I think, but I'm open to correction.

I mean no disrespect and I don’t mean to offend, I was just asking.
I agree making a “plug” would be nice.
I’m concerned I don’t have the skill to make a IDENTICAL test plug that would be worth the time, I’m thinking I’ll make the backplate threads too small (ID) and bit by bit open it up until it’s perfect (or close)

texasgeartrain · Aug 21, 2020

The msc direct prices are kind of high. The ebay price is ok I think, and I have used these. The material is cast iron-ish

. But whatever material is mixed into it, its real hard to cut. Even drilling holes and tapping is possible, just not as pleasant as other material.

8" :
8" Semi-Machined Threaded Back Plate 2-3/8"- 6 For All Plain Back Lathe Chuck A | eBay

10" :
10" Semi-Machined Threaded Back Plate 2-3/8"- 6 For All Plain Back Lathe Chuck R | eBay

Now I forget all the how to's and why, but Kevin T had purchased a 10" from ebay, pretty sure 10" anyway, and either didn't want to cut OD all the way down to something much smaller, or maybe material was too hard, I forget. But he picked atleast one up from SBLatheman as I recall. He may have more also, but I'm not sure the cost or what he has in inventory.

Be pretty cool if Kevin T commented, but I think he's worried about the covid. Hey Kev, buddy, its the internet, you don't even need a mask.

Derek Smalls · Aug 21, 2020

Homebrewblob said:
I’m concerned I don’t have the skill to make a IDENTICAL test plug that would be worth the time, I’m thinking I’ll make the backplate threads too small (ID) and bit by bit open it up until it’s perfect (or close)

You're concerned that you don't have the skill to cut an external thread, on a piece of scrap metal which can be tossed if you mess it up, taking as many tries(and pieces of scrap) as you need to get it right, BUT, you're confident you can cut an internal thread correctly in a piece of material you need to purchase for the job, checking the fit by removing the entire chuck and work piece every time? I'm not trying to be rude but you may want to rethink that.

Homebrewblob said:
3 I have a simple indexable threading tool (I have NO HHS) will this work or do I need a Specific threading geometry?

Not sure what exactly you are describing here, is it an insert specifically designed for internal threading, or a turning/boring tool with a 60* corner? The latter will not work well, if at all.

Advice (for novice) building 1st 1957 southbend backplate!! Thanks!

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