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Thread: SB7 Shaper Crossfeed Screw
07-13-2009, 09:45 AM #1
SB7 Shaper Crossfeed Screw
I´m halfway in my shaper restoration, and I´m cutting a crossfeed screw (was missing).
All I had was the nut, and doing my best to measure it I concluded it´s a 0.5" 10tpi ACME screw.
I cut the thread as per specs (machinery´s handbook), tool ground to 29deg, set square and at center height, external and internal diameters correct.
Although the screw fits the nut, it just doesn´t feel right. It starts very loose, and when it´s almost thru the nut it becomes tight (it´s the same threading from both ends of the nut). Still, I´m able to slightly tilt the screw inside the nut.
It gives me the impression that there are very few contact points between the screw and the nut, as if there was a slight pitch error or a thread angle error.
Would another SB7 shaper owner be so kind to confirm this thread specs? Is it really 0.5in, 10tpi and ACME form?
07-13-2009, 11:27 AM #2
Yes, the standard shaper has a 1/2-10 acme. But SBL also made these with METRIC threads. Does your nut have an "M" stamped on it?
07-13-2009, 11:37 AM #3
You could just buy that from McMasterCarr.
"It starts very loose, and when it´s almost thru the nut it becomes tight"
This is a sign that your lathe tool is pushing on the shaft. Take some spring passes to help with that and also give the shaft some support with a steady or follow rest.
Or that you are cutting the incorrect pitch.
07-13-2009, 12:49 PM #4
I turned it between centers, using both a steady rest (close to the dog) and a follower rest. I´d rule out anything related to flexing.
the nut does have a big "M" stamped on it. I think you solved it, thanks a lot. I´ll try again with 2.5mm pitch and 30 deg angle.
There is also a "S" inscribed in a square.
Together with the "M", probably reads "It´s Metric, Sucker!"
07-21-2009, 06:19 PM #5
I poured some hot-melt glue inside the nut and was able to confirm it was metric, just as Ted said it was.
12.5mm diameter, 2.5mm pitch (not a standard trapezoidal size, as far as I know). Sharpened another tool to 30 deg and cut another screw.
Worked like a charm, smooth and no play. Made a bronze bushing and a thrust washer, thinned a brass nut and added a stainless acorn nut.
One less part to go, thanks again.
07-22-2009, 11:07 PM #6
You are going to need a spring washer under the acorn nut if you want your feed paw to ratchet properly. With the spring washer missing the feed rod will rock back and forth without advancing to the next tooth. You will also need a jam nut to lock the acorn nut to the shaft. See items 1,2 and 52 below.
Let me know once you get this so I can replace the picture with a link. Do a right click and save as to copy to your computer.
Last edited by Paula; 07-23-2009 at 04:39 AM. Reason: Post large images as a link
07-23-2009, 10:32 AM #7
thanks for the good info on the spring nut, makes sense. I had thought that simply adjusting the torque on the nut would suffice to attain the proper friction, but a spring washer should work much better.
I already included a jam nut, the brass nut on the pics that goes with the acorn nut.
Thanks for the image, I had downloaded and hard-printed this book, but missed the spring washer.
07-23-2009, 05:10 PM #8
Here are the rest of the forms for the shaper if you need them.
I will post a few update pictures on my shaper soon. I have it very close to being done. I just need a gib ,knob and a little vise work. That VFD I installed on the shaper is very nice. I have been busy with a few other things so the SB stuff got pushed back.
I knew I was pushing my limits with the large picture above...I thought it would at least make it till this evening. Nope!
It sure is hard to slip anything by that gal.
Thanks Paula for keeping us on a tight line.
07-24-2009, 12:18 PM #9
Thanks again, Don.
BTW, this little shaper seems pretty repair-unfriendly.
The oil system is a nightmare to disassemble/clean, parts that should be simple to remove (e.g. vertical feed nut) require dismantling the whole machine, even the gib screws are different from everything I´ve seen (7/32in, 28tpi).
The toolpost locking screw was bent on mine, had to turn another one to replace, couldn´t find anywhere.
07-24-2009, 03:05 PM #10
I also need to make that thumb screw for mine. The thread is called a 12-28 and used to be a popular thread. You did a good job on making a new one. I was going to look for other examples of the knob before I made mine. To keep the machine looking close to original in looks. But now I do not need to do that. Yours looks very close to mine.