Survey on Sieg 7" lathe - Bazmak

[ShopShoe]

bazmak,

I'm following this thread and I have a 7x lathe. I have had to address this problem at least twice.

I can also say that I was originally plagued by gib screws continually working loose, which has also been mentioned by many owners of these lathes. Better-quality screws and nuts and sometimes new tapped holes are needed.

I am conservative when it comes to modifications. I start slowly and work up to "better" a step at a time and things really do get there in the end.

Back to the problem in hand: I don't have the measurements to hand, but my lathe's problem is that the measurements vary depending on the distance along the bed (14-inches in my case). It appears to "belly" near the tailstock end, like the lathe here:

http://madmodder.net/index.php?topic=627.0

(Too bad the photos have been moved)

In addition, the serial number stamping distorted the bed in that area.

My next major effort at improvement will be an attempt to totally disassemble the lathe and attempt to actually determine whether the bed can be improved by scraping, maybe even grinding, but this may end up proving I need a new bed.

Meanwhile, things with this lathe are OK enough for my present operations that I can do well in my usual work envelope near the headstock: I only have to worry if I would want to turn a long length between centers, which I seldom need to do.

So, I originally made a part like yours and that was good enough for about a year. The next iteration included a remake of both sides, lapping and shimming: Better. If I can determine the bed is workable or end up with a new bed, then I will probably go the tapered-gib route.

If you haven't read this, also see here:

http://www.homemodelenginemachinist.com/showthread.php?t=8306&highlight=Beginning+Mini-lathe

I can also recommend the Connolly book. Not used every day, but worth having to see what would be done in a perfect world (circa 1954). It is a good idea to get the whole theory down, otherwise it is possible to "correct" via a compensation that creates another need for a compensation-for-the-compensation further down the road.

I have been following your various projects and I have no doubt you will do something and I will be watching whatever you post on this.

--ShopShoe

 

[bazmak]

Do me a favour shoeshop.When you have time please check and post the 3 dims requested.Next time you reove the apron and disconect the leadscrew
set the gibs to a nice sliding fit and then twist the carriage ACW and CW let me know if there is much play. Regards Barry

 

[ShopShoe]

bazmak,

I've just been out to the shop for the measurements. I believe I am measuring what you asked for, but I could also be confused.

1. The width of my bed varies from 3.244 to 3.247 inches over the length of the bed, measured in five places multiple times. Just as I said, the larger measurement is at the tailstock end, near the area where the serial number is stamped.

2. The milled-out area of the saddle (carriage) measures from 3.322 to 3.326. I do not have an extremely accurate way to measure this in the center of the saddle and I do know that the outer ends are "bell-mouthed" a little (lets say the outermost 3/16-inch).

3. Using feeler guages, I get something like 0.039 gap in the front and 0.032 in the rear. Once again, I wish I had a more accurate way to measure this. After earlier work, I have the main travel of the saddle located and stabilized by the front and back of the prism. My carriage does not try to climb up the prism as you were describing. My front gib clears the rack and gear by a good margin.

4. With the saddle sliding freely and smoothly, but not yet as uniformly as I would like, and checking movement with a dial indicator, I can get the back side to lift a maximum of 0.0015 at the loosest point. I can not get the front side to change more than 0.0005 under considerable pressure, which I consider good for this lathe at this point in time. The important thing (to me) is that the amount of slop that shows up at the tip of the cutting tool is very minimal in the normal direction of rotation.

I believe that I can eventually get the bed evened out more (or replace it) and then put in the tapered gibs and get this even better.

I hope this is what you were looking for.

 

[Brian40]

Hi Bazmak
You may find some of the work on my site handy (see bottom of page) feel free to down load any of the PDF's you think handy, the one on adjustable gibs may be of particular interest. I am always available to help.

I haven't Touched the gib's on my lathe for three years and it is worked hard with a 1HP motor
If you look at my 32x40 H gas engine thread you will see just how hard.
Brian.

 

[bazmak]

Many thanks Brian,just had a quick browse.Many thanks for the PDFs very interesting and opened up some problem areas that i have thought about
that you have appeared to have solved.I like the gibb plts with top adjustment screws and will make a decision on your idea pr try tapered gibs now that i have a mill.I like the cross slide nut mod and may try screwcutting a new lead screw for the the cross slid mod.I did the extended cs travel to the front but
as yet have not found a need for the rear ext. travel.Again many thanks
will post if i do any of your mods. Regards barry

 

[zoltan]

I agree with the other posters here, that you really want the prism locating the carriage and not the back edge of the bed. However, the carriage gibs need to be adjusted well for the prism to do its job.

While tapered gibs would be great, I went a cheaper and easier route which has worked very well for me. I found the biggest problem to be the stock gib adjustment system. It's super difficult to get adjusted correctly and go out of adjustment super fast; it sucks. I removed the small set screws and tried different shims (I use feeler gauge leafs as shims) between the carriage and gib until I found ones which just allowed easy movement. Now everything is nice and tight and solid.

http://benchtopmachineshop.blogspot.com/2014/04/lathe-shimming-carriage-gibs.html

Also, if you want to easily increase the rigidity of your lathe, replace the compound slide with a solid block of steel; I only ever used the compound for threading anyway. That cheap mod alone will help a lot.