Lathe Compound

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asallwey
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Location: N. Virginia

Lathe Compound

Post by asallwey » Mon Feb 01, 2021 9:34 am

I'm about to work on my compound to replace the leadscrew. There are 2 things I would like to address if they don't turn into too much additional work. The attached pic shows the areas of concern.
20210201_081910_rs.jpg
#1 My current setup has 2 locking washers that hold the screw in place. What do more robust, old-school, American made, etc. machines do to hold the screw in place and adjust for thrust or backlash? I will need new ones as these are metric.

#2 The handle is held on by a cap screw. Again, what do more ... use to hold the handle? I think a key would be a big help.

Pictures of machines don't really help me in this case because they don't go into the 'assembly detail' that I'm looking for.

Thanks,

Alex

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Gary Armitstead
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Re: Lathe Compound

Post by Gary Armitstead » Mon Feb 01, 2021 1:39 pm

There should be a Woodruff key in that assembly somewhere.

It would also help to know the "brand name" of your lathe and the country of origin as far as manufacturer.
Gary Armitstead
Burbank, CA
Member LALS since 1980
Member Goleta Valley Railroad Club 1980-1993

asallwey
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Re: Lathe Compound

Post by asallwey » Mon Feb 01, 2021 2:30 pm

Gary Armitstead wrote:
Mon Feb 01, 2021 1:39 pm
There should be a Woodruff key in that assembly somewhere.

It would also help to know the "brand name" of your lathe and the country of origin as far as manufacturer.
You mean for the handle like I mentioned above?

It's a 1998 Shoptask from China. Not sure how that helps with describing how other machines accomplish controlling backlash and keeping the handle on.

Russ Hanscom
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Re: Lathe Compound

Post by Russ Hanscom » Mon Feb 01, 2021 2:45 pm

Normally the handle is keyed to the shaft and the nut or screw is only used to control backlash. It appears that you do not have the original handle?

asallwey
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Re: Lathe Compound

Post by asallwey » Mon Feb 01, 2021 2:48 pm

It is the original handle, that is how they did it. A cap screw rather tight. I've been thinking of using a key when I install the new screw.

Russ Hanscom
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Re: Lathe Compound

Post by Russ Hanscom » Mon Feb 01, 2021 3:55 pm

Well, that is definitely one difference between a quality lathe and yours. All the ones I have known have a keyway. If you add a keyway, then the nut or screw does not have to be extra tight. Is the dial keyed or floating? With a key, you could allow the dial to be loose enough to adjust its setting - nice to be able to zero it when starting a cut.

pete
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Re: Lathe Compound

Post by pete » Mon Feb 01, 2021 6:26 pm

I guess it depends on just how deep you want to get into correcting some of the original design choices made on that lathe. But I'd start by going through some older machine manuals of high quality lathes. The Old Wood Working Machine's (OWWM) website has quite a few here, http://vintagemachinery.org/ Manufacturer's such as Rivett, Hardinge etc would be where I'd start. Rivett to mention just one used a rather clever locking method for there machine dials that works and has much less chance of disturbing the feed screws rotation while locking the dial. George Thomas in the UK went to some effort to duplicate the Rivett and a few other manufacturer's methods on his Myford Super 7 in this book, https://www.teepublishing.co.uk/books/i ... op-manual/ Ending up with something that does work reliably every single time takes some fairly precise measurements and machining.

Ideally you'd want both a ball or needle thrust bearing and the hardened and ground washers decent thrust bearings always use as well as one or two ball or needle bearings to take the radial loads. And as mentioned a better design for attaching the handle to the screw end using well fitting keys. Adding all that in while trying to adapt a stock replacement screw with shop machined extensions to fit those bearing additions, keys etc wouldn't be all that easy and takes a fair amount of design and machining experience to end up with any real improvements over what you already have. Myself I think I'd start with a good brand name Nook, Roton or better blank feed screws and nuts with some level of guaranteed accuracy. Back lash between the screw and nut is only part of the problem. Yes this is on a Shop Task machine so it's highly debatable on how far to go, but the following information is still correct for any machine tool. ALL feed screws and nuts including the worlds best will always have various degrees of measurable screw pitch lead/lag errors in them. And no matter how good the screw and nut might be, your still going to have to contend with at least some backlash. Any new replacement screw and nut is only going to reduce it but not eliminate the problem. Bridgeport as one example did and may still do guarantee there new machines to have a maximum of .004" back lash. So unless your machine has half a turn or more of back lash due to wear, it's a fair amount of money to reduce it without completely eliminating the problem. There were also quite a few machines at the cheaper end that don't have any method of adjusting the nut clearances on the screw. Depending on the design, some can be partially split to make them adjustable and remove high amounts of back lash. So I'd check that first.

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Gary Armitstead
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Re: Lathe Compound

Post by Gary Armitstead » Mon Feb 01, 2021 7:23 pm

asallwey wrote:
Mon Feb 01, 2021 2:30 pm
Gary Armitstead wrote:
Mon Feb 01, 2021 1:39 pm
There should be a Woodruff key in that assembly somewhere.

It would also help to know the "brand name" of your lathe and the country of origin as far as manufacturer.
You mean for the handle like I mentioned above?

It's a 1998 Shoptask from China. Not sure how that helps with describing how other machines accomplish controlling backlash and keeping the handle on.
Gee, sounds like a little bit of "hostility" to me with your comment "Not sure how that helps with describing how other machines accomplish controlling backlash.....".

That said, I WAS trying to narrow down more info on this lathe you have so we could better answer your question. First of all, your machine is from China and they cut corners in manufacturing all the time. I have operated many different lathes and mill in my 55+ years in the machine trades. A woodruff key is very commonly used to do exactly what you are trying to allege. Adjust backlash, but keep the dial and handle snug. Do you have equipment to machine a woodruff key slot on the leadscrew? Woodruff keys come in all sizes and these sizes are numbered as follows:

https://www.engineersedge.com/hardware/ ... _15008.htm

If you're going to do this yourself, you will need to get a woodruff key cutter and set this leadscrew up in a mill and cut it. The key size will depend on the shaft diameter.

I have a Clausing/Atlas Commercial 12X36 lathe in my shop and I just replaced all the graduated dials on the compound. ALL of the dials had woodruff keys.
Gary Armitstead
Burbank, CA
Member LALS since 1980
Member Goleta Valley Railroad Club 1980-1993

asallwey
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Re: Lathe Compound

Post by asallwey » Mon Feb 01, 2021 9:38 pm

Pete, thanks for the leads. I will go back to OWWM, haven't been there in years and kind of forgot about it. I realize the limitations of my machine but this is one of those jobs I've put off for a long time. My compound screw has a bend in it, just before the rear plate with the oiler. I've tried several methods of straightening it, and getting a replacement, with no success. I have a new 10 tpi screw 10" long coming, and which will change it from 20 tpi. I've cleaned up all but the dovetails on the surface grinder, and hope to begin working on it soon. I figured this is the time to make changes if I can. The dial is floating, and the center is keyed. It's too bad the keyway didn't continue to the end of the shaft. I'm not thrilled with the double nuts, although they do work. Thanks for taking the time.

Gary, that's a good and timely reference as I was giving serious thought to putting a keyway in the new shaft out to the handle, for the benefits Russ pointed out. Quite often when folks see China on a lathe it turns to a lot of bashing, rather than constructive help. I appreciate you keeping on the help path.

Thanks guys!

asallwey
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Re: Lathe Compound

Post by asallwey » Tue Feb 02, 2021 9:08 am

Pete,

I ordered the George Thomas book. I haven't bought a machining book in years so about time. Only used copies, but they say other than some wrinkles on the cover, the inside is like new.
Ideally you'd want both a ball or needle thrust bearing and the hardened and ground washers decent thrust bearings always use as well as one or two ball or needle bearings to take the radial loads.
I was looking over my parts and realized that I had a needle thrust bearing between the back plate and the dial unit. I didn't use the ground washers, don't remember why, maybe not enough room.
Myself I think I'd start with a good brand name Nook, Roton or better blank feed screws and nuts with some level of guaranteed accuracy.
The new screw is coming from: http://www.zyltech.com/1-2-10-acme-carb ... ths-10-72/. I don't know if they machine it or, but I think so. Not precision grade, but a good choice for this machine. Their nut won't work, but I have a disk of bronze and I ordered their tap. This screw is about 0.020" larger od than original, so I'll modify the back plate to accommodate. I'll also consider placing the thrust bearings inside the plate. And if I keep the double nut approach I might just make a cover to I don't have to look at them.

I watched a video (2 actually) by Stefan G on reworking a compound, and he put a double row angular bearing in the back plate for the screw. I might consider that also. And with all the bearings stuffed in the back plate, I'll probably have to make a wider/deeper one. :)

I'm just trying to get my compound to move smoothly, be nice to use it occasionally for more than rotating my qc toolholder.

Alex

pete
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Re: Lathe Compound

Post by pete » Tue Feb 02, 2021 8:56 pm

I think you'll find that GHT book is one of the better one's around Alex and well worth what ever it costs. But there's a whole lot of machining books being resold on Ebay at ridiculous prices. I've found it much cheaper to by anything published in the UK from here. https://www.teepublishing.co.uk/books/in-your-workshop/ Other than for taper turning or during single pointing threads there's good logical arguments for removing the top slide completely and using a solid spacer block to mount the qctp to it. Stefan and a few others have done exactly that. Afaik ball or roller thrust bearings don't work that well without the hardened and ground washers since the balls or rollers tend to chew up anything softer once there preloaded and the clearances are reduced to zero.

John Hasler
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Re: Lathe Compound

Post by John Hasler » Tue Feb 02, 2021 9:20 pm

Alex writes:

I watched a video (2 actually) by Stefan G on reworking a compound, and he put a
double row angular bearing in the back plate for the screw. I might consider that also.

They may be relying on slop in the bearing to keep the screw from binding.

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