Sieg SC4: Question about carriage feed mechanism?

[Jus Lurning]

Hi,
I have been trying to compare and contrast the Sieg SC4 lathes with the Precision Matthews 1022/1030.

The Precision Matthews 1022/1030 utilizes a key way drive system for carriage feed operations when you are not cutting threads.

I have not been able to learn what sort of mechanism is employed by the Sieg SC4 to motivate the carriage feed.

Does the carriage feed for basic turning on the Sieg SC4 rely exclusively on the half nut engagement, or is there a "key way drive" for carriage feed when you are not specifically cutting a thread?

Thank you!

 

[higgite]

I have an LMS 3540, which is an 8x20 SC4 built to LMS specs. It has two power feed levers and one lead screw. Both levers engage the same half nuts with the one lead screw. The lever on the right side of the carriage is geared internal to the carriage to produce a little less than 1/5 the feed rate as the front lever. The intention is to use the front lever for roughing and the side lever for finishing when the change gears are set up for turning. Only the front lever is used for threading when the change gears are set up per the threading chart.

The side lever also controls the cross slide power feed.

Tom

 

[Jus Lurning]

Hi Tom,
Thank you for the helpful information.

Is the lead screw threaded around its entire circumference or is there a key way groove running the length of the shaft? I am trying to learn more about the mechanism that is engaged by the "Power Feed handle" (as per LMS user's guide description) which is also known as the "X or Y axis auto feed change handle" (as per the Travers Tool user's guide and installation manual description).




Your explanation about the gear reduction was very helpful. It guided me to recognize where some of the SC4 user guides refer to this.

The Travers Tools guide explains "In the lower position, the X-Y Auto Feed lever moves the carriage along the ways, much like the Power Feed lever, but at a slower speed."

The LMS guide describes specific turning feed rates in a chart that references the gearing. After reading your note I was able to compare the LMS description between the power feed rate and the threading rate and recognize the 1/5 rate of reduction.

For example; the LMS guide cites the feed rate for turning with "fine feed" as 0.0018"(0.045 mm) per revolution when the gears are configued as A=30, B=120, C=60, and D=120.
I looked in the threading chart to find a comparable gear configuration and found that when the gears are in the same A=30, B=120, C=60, D=120 configuration and the Half Nut lever is engaged the feed rate is 0.25mm per revolution.
0.25mm/0.045mm = 5.5555, which is the 1:5 ratio you mentioned. Thank you for helping me recognize this idea.

Thank you!

 

[higgite]

You’re quite welcome. Glad I could help. And welcome to the forum.

The lead screw is fully threaded, no longitudinal groove.

Here’s a link to a manual supplement that is also worth a read.

http://www.g4ztd.info/pdfs/Bob%20Ackert's%20SIEG%20SC4%20Manual%20Supplement%20to%20SIEG%20SC4.pdf

Tom

 

[Jus Lurning]

Thank you for sharing the link to that supplement. I smiled when I read that Mr. Ackert illustrated the gear reduction ratio many years before I figured it out. .

Thank you!