Author Topic: Leadscrew  (Read 2457 times)

Offline steamer

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Leadscrew
« on: March 23, 2019, 02:51:02 AM »
Gotta make a leadscrew for a lathe at work.    Derbyshire 750     #12-20 LH   ( 0.2185 x 20 threads per inch)  I'll need to make a tap and a nut for it too.....I'll post once I've gotten started....

Dave
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Offline scc

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Re: Leadscrew
« Reply #1 on: March 23, 2019, 09:05:30 AM »
 :popcorn:

Offline steamer

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Re: Leadscrew
« Reply #2 on: March 23, 2019, 11:06:47 AM »
Funny that....it's actually measures larger than the #12 standard, and closer to a 5.5 mm  x 20 threads/inch.  :insane:    Lathe manufacturers did that to prevent the hacks from making parts that they could just "BUY" from them....Waltham W20 collets were 20mm x 1.66667 mm pitch buttress thread on their collet draw bars....a real odd ball..but doable if you think about it for a minute.    The challenge is going to be supporting the thread as I cut it.   Time to break out the follower rest.    I'll need to worry about the burr I'll throw up as I cut this thread, as it will interfere with the follower rest...so I'll have to wade into this a bit.   Should be a good challenge as the screw is about 5" long...

But I'll make the tap first.....then the nut, and then the screw to fit

My son has been sick for the last 3 months...but hes feeling better right now, and I think he wants to go practice today....so that's on the agenda I think.

Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
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Offline simplyloco

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Re: Leadscrew
« Reply #3 on: March 23, 2019, 11:11:08 AM »
May I suggest that burrs will be minimised if you cut on the flank with the compound slide set to the thread angle?
John

Offline steamer

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Re: Leadscrew
« Reply #4 on: March 23, 2019, 11:15:13 AM »
May I suggest that burrs will be minimised if you cut on the flank with the compound slide set to the thread angle?
John

Absolutely, as is the correct way.   I'll still need to clear the burr every pass though.   

Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
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Offline steamer

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"Mister M'Andrew, don't you think steam spoils romance at sea?"
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Offline b.lindsey

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Re: Leadscrew
« Reply #6 on: March 23, 2019, 12:00:46 PM »
Well that should keep you busy a few hours :). Glad to hear William is feeling better too Dave.

Bill

Offline Don1966

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Re: Leadscrew
« Reply #7 on: March 23, 2019, 03:26:22 PM »
Ok Dave I am in on this one to see how you go about it. Glad to see William is doing better bud!

Don

Offline steamer

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Re: Leadscrew
« Reply #8 on: March 23, 2019, 09:31:47 PM »
I'll be making a new bearing as well.   The existing bearing is screwed together and then staked.    It is NOT going to come apart...no matter how I try

So I'll be drawing the whole thing up, meanwhile, I have a project for Kim I need to do

Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
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Offline steamer

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Re: Leadscrew
« Reply #9 on: March 23, 2019, 11:07:11 PM »
Here's the assembly that will not come apart....

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Offline steamer

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Re: Leadscrew
« Reply #10 on: March 23, 2019, 11:10:06 PM »
And a sketch of the outside of the bearing mount.

I'll need to sort out the geometry internally now

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Offline Neil-Lickfold

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Re: Leadscrew
« Reply #11 on: March 24, 2019, 06:18:08 PM »
Cut the lead screw first, and before cutting the lead screw, also make the blank for the tap at the same time. IE the final tap. You can measure the thread diameter with wires etc, unless you are buying acme 20tpi threading inserts  that are the full form. You can keep threading until you get to the measured OD.
Making series taps, so ones that are the same but just smaller on the over all dimensions help to get a really nice neat thread form as well.
After heat treatment the tap will be ever so slightly larger in diameter, and will make a really neat nut to lead screw. On the leadscrew, just deburr and put a small corner break on the outer edges of the thread form. But not on the tap. Leave the tap outer edges sharp.
Neil

Offline steamer

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Re: Leadscrew
« Reply #12 on: March 25, 2019, 12:37:40 AM »
Cut the lead screw first, and before cutting the lead screw, also make the blank for the tap at the same time. IE the final tap. You can measure the thread diameter with wires etc, unless you are buying acme 20tpi threading inserts  that are the full form. You can keep threading until you get to the measured OD.
Making series taps, so ones that are the same but just smaller on the over all dimensions help to get a really nice neat thread form as well.
After heat treatment the tap will be ever so slightly larger in diameter, and will make a really neat nut to lead screw. On the leadscrew, just deburr and put a small corner break on the outer edges of the thread form. But not on the tap. Leave the tap outer edges sharp.
Neil

That was the plan Nick.   Bearing and retaining components first, then the tap and then lead screw.  I made the components, and made the toolmakers tap, something I've had very good luck with in the past.   I've attached the component drawings I did this morning....They are not my best drawings, but they're as detailed as they need to be.....I also attached some photo's of the bearing block, the retainer, and the tap.   I'll wire brush it tomorrow at work.   Then tomorrow night, I'll cut the nut blank, and then use it to fit the leadscrew.    Tidy it up and attach the nut to the cross slide and we'll be in like Flynn!

"Mister M'Andrew, don't you think steam spoils romance at sea?"
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Offline steamer

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Re: Leadscrew
« Reply #13 on: March 25, 2019, 12:40:52 AM »
Here are the pics
The bronze end play nut has a 3/8-40 thread.   I've made a wrench for it too.   Once I have it adjusted, I'll stake the nut with a punch.

Dave

"Mister M'Andrew, don't you think steam spoils romance at sea?"
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Offline steamer

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Re: Leadscrew
« Reply #14 on: March 25, 2019, 12:59:43 AM »
Nick, the thread is a 60 degree V thread,   0.217-20 LH.    I won't be buying a section of acme shaft for this one!....No taps out there commercially available either.

I just got to Make it happen!

Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!