Model Engine Maker

Supporting => Tooling & Machines => Topic started by: steamer on March 23, 2019, 02:51:02 AM

Title: Leadscrew
Post by: steamer 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
Title: Re: Leadscrew
Post by: scc on March 23, 2019, 09:05:30 AM
 :popcorn:
Title: Re: Leadscrew
Post by: steamer 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
Title: Re: Leadscrew
Post by: simplyloco 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
Title: Re: Leadscrew
Post by: steamer 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
Title: Re: Leadscrew
Post by: steamer on March 23, 2019, 11:18:04 AM


http://www.modelenginemaker.com/index.php/topic,649.msg6073.html#msg6073
Title: Re: Leadscrew
Post by: b.lindsey 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
Title: Re: Leadscrew
Post by: Don1966 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
Title: Re: Leadscrew
Post by: steamer 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
Title: Re: Leadscrew
Post by: steamer on March 23, 2019, 11:07:11 PM
Here's the assembly that will not come apart....

Title: Re: Leadscrew
Post by: steamer 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

Title: Re: Leadscrew
Post by: Neil-Lickfold 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
Title: Re: Leadscrew
Post by: steamer 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!

Title: Re: Leadscrew
Post by: steamer 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

Title: Re: Leadscrew
Post by: steamer 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
Title: Re: Leadscrew
Post by: Neil-Lickfold on March 25, 2019, 08:27:26 AM
With the toolmakers tap you can make them with 2 or 3 flats.
I make them with 4 flats, and then do a relief grind up the side if it needs
any positive cutting.
Unless it is a large diameter tap, then I just make a series of cuts up the tap, and relieve
the od of the tap off the high point to reduce the drag.
I like using the full form inserts for the tpi or the thread pitch.
Very nice and thanks for the pics.
There is no point in putting in a lot of time if it is only a 1 time only thing as well.
Sometimes depending on how long the nut it etc, it can be viable to screw cut the thread than to make a tap.

Neil
Title: Re: Leadscrew
Post by: steamer on March 25, 2019, 10:04:45 AM
 I usually do 3 flats on a 20 degree angle.  This one might need a longer taper..  I milled this taper in on this one, but if it needs lengthening, ill just grind it.
Title: Re: Leadscrew
Post by: steamer on March 26, 2019, 02:28:35 AM
Productive night on the leadscrew front!    I tapped the nut, and it cut like buttah!   On to the screw.

I started bringing the 5 inch long screw to size, and it was bowing pretty bad, even with a left side turning tool to put the cut force along the axis of the part.  So I needed a follower rest.

Problem is the stock SB one is far too big for a part this size, and it is also far to wide.   So I mounted a angle plate to the T slotted saddle, and mounted up a scrap piece of bronze with a notch cut in it.

I have to readjust the follower rest for every cut, but I'm only chasing the last 0.020.   There's a little taper I'm dealing with  about 0.002 over 5 inches...I'll take that out with the TS...but I'm done for tonight.

Dave
Title: Re: Leadscrew
Post by: Neil-Lickfold on March 26, 2019, 04:54:46 AM
I always try and have the follower on the fresh cut material. But it is a 2 way thing. The chips can easily get in the way.
Its a pain, but running a vacuum cleaner to draw away the chips works really well.
I put my compound on an angle, Normally 30 deg, so that  the value on the cross slide, now becomes the diameter of the cut.
But it gets worse as you have to reset or bring into the job the steady.
I find that the Myford travelling steady often just gets in the way.
Sometimes it is also easier to cut a longer blank, to give room for the tools etc, and then set up and cut the excess off later when
the end detail is being finished,
It is small jobs like this that I think I should make up a roller box.
But like you have just persevered and made do with what was available at the time.
Neil
Title: Re: Leadscrew
Post by: simplyloco on March 26, 2019, 09:44:34 AM
Very interesting and very small! When I did the 1.00 mm pitch reverser on my Britannia I gave myself a challenge and screw cut the LH thread bronze nut in the lathe! If anyone is interested here is a link to a couple of pics.
John
http://modeleng.proboards.com/thread/3571/brit-progress-screwcutting-reverser
Title: Re: Leadscrew
Post by: steamer on March 26, 2019, 11:28:59 AM
This one was a challenge.....the tool clamp screw is 4-40.    0.354-10 LH ACME

http://www.modelenginemaker.com/index.php/topic,1192.msg15322.html#msg15322
Title: Re: Leadscrew
Post by: steamer on March 26, 2019, 11:44:17 AM
I always try and have the follower on the fresh cut material. But it is a 2 way thing. The chips can easily get in the way.
Its a pain, but running a vacuum cleaner to draw away the chips works really well.
I put my compound on an angle, Normally 30 deg, so that  the value on the cross slide, now becomes the diameter of the cut.
But it gets worse as you have to reset or bring into the job the steady.
I find that the Myford travelling steady often just gets in the way.
Sometimes it is also easier to cut a longer blank, to give room for the tools etc, and then set up and cut the excess off later when
the end detail is being finished,
It is small jobs like this that I think I should make up a roller box.
But like you have just persevered and made do with what was available at the time.
Neil

I leave my compound at 29, but the tool aligned.   They both get it done in my book
I don't want to turn this project into a tool making exercise...I just want to get it done.  So I'll leave the tooling crude...but effective.

The original screw is cut long, I suspect for the same reason...to have some travel for the follower rest before the tool gets to the TS center.  Mine is also.

Dave
Title: Re: Leadscrew
Post by: steamer on March 27, 2019, 11:24:57 AM
I"m done!

Here's the family shot, new one mounted, and old one next to it

I've got some more in process ones...but I have a job to go to.....perhaps later

The screw was a bit of pain in the rear, as it has a very long nut, and any pitch error was immediately apparent.     So it was slow going with light cuts to bring it in.

Dave
Title: Re: Leadscrew
Post by: b.lindsey on March 27, 2019, 01:09:05 PM
Well done Dave. Hope the boss appreciates all the effort that went into it!!

Bill
Title: Re: Leadscrew
Post by: steamer on March 27, 2019, 01:11:22 PM
Well done Dave. Hope the boss appreciates all the effort that went into it!!

Bill
Well   me too.   But I doubt it.
Title: Re: Leadscrew
Post by: Vixen on March 27, 2019, 01:47:26 PM
Nice one Dave,

"The jobs a good 'un"

Mike
Title: Re: Leadscrew
Post by: Don1966 on March 27, 2019, 01:52:06 PM
Love it Dave!.... :ThumbsUp:


 :cheers:
Don
Title: Re: Leadscrew
Post by: steamer on March 27, 2019, 04:53:10 PM
If I ever do this again .   Ill use hardened steel for the follower.Bronze wore too fast.
Title: Re: Leadscrew
Post by: Tennessee Whiskey on March 27, 2019, 06:41:32 PM
You go boy: damn good job 👍

Cletus
Title: Re: Leadscrew
Post by: stevehuckss396 on March 27, 2019, 07:43:13 PM
I"m done!


Never doubted you for a second. Way to go sir
Title: Re: Leadscrew
Post by: steamer on March 27, 2019, 09:25:54 PM
OK   a few in process shots.....I also made a new nut, a "P" shaped affair....not much photo evidence on that, but I was in "bull in the woods" mode ...12 hour day yesterday

Anyway...a few more shots that seem pretty self explanatory.

To cut the thread, I left the cross slide locked and just moved the compound to add feed.   That allowed the follower rest to stay in position.    I also left the half nuts closed, and just used the VFD to crawl into position.   I had thread reliefs on each end, so that simplified everything.

If I had to do this again, I'd make a cross slide mounted follower that had HSS lathe blanks to bear against the part.  The bronze just wore too fast.   I ended up dressing the surfaces on the mill 3 times to make that screw....and as it wore, the screw would push away..  It was tedious.

Always take a scratch cut...and Always check it with a thread gage.....ALWAYS!

Dave



Title: Re: Leadscrew
Post by: steamer on March 27, 2019, 09:30:00 PM
And Another thing

The tool is a "thinbit" threading insert, that fits in my new grooving tool.   It cuts the nicest finish!....I had polished chips coming off 0-1 tool steel, which can be tough to get good finish on unless the tool is really good..    Now I'm old school and never really used insert tooling in my shop....If I needed a threading tool, I usually grabbed a blank HSS bit and got cracking grinding one and checked it on a "Fish Scale"  ,,,,but not anymore!

Thanks for turning me on to those Steve Huck!

Dave
Title: Re: Leadscrew
Post by: steamer on March 28, 2019, 01:58:11 PM
I checked the assembly    total backlash installed    0.003"....a good deal better than 0.019"!
Title: Re: Leadscrew
Post by: Maryak on March 28, 2019, 07:52:33 PM
 :cheers:
Title: Re: Leadscrew
Post by: steamer on March 31, 2019, 03:10:46 PM
A vid of the threading operation ...about 1/2 way into it.

https://www.facebook.com/mcandrew.piper/videos/2268228856787841/?t=2

Dave
Title: Re: Leadscrew
Post by: Dave Otto on March 31, 2019, 04:55:05 PM
Looks good Dave!

Dave
Title: Re: Leadscrew
Post by: steamer on March 31, 2019, 04:57:46 PM
Looks good Dave!

Dave

A hardened steel follower rest that mounts on the cross slide is on the list of accessories I'm going to build...