Warco Saddle Stop

[Papa Smurf]

I have yet to find an answer for the existence of 2 means of powering the carnage up and down the ways, lead screw and gear rack. Any thoughts would be appreciated. Thanks
Eric

Apologies for my tardy reply, but I don't see any other answer to your question. I trust that your use of the word "carnage" is a typo and not an accurate reflection on the "good condition" machine you bought!

Most "professional" manual lathes have both rack and leadscrew features fitted. Some very small lathes may dispense with the rack, and their leadscrews are permanently coupled to the saddle - a handwheel on the end of the leadscrew moves the carriage. Once we get to CNC machines, all bets are off.

RACK:
A handwheel on the apron drives the lathe saddle through some gearing which ends in the pinion that engages with the rack. This provides for "quick and dirty" movements of the saddle along the bed, irrespective of whether the lathe spindle is rotating or not. I have also seen some lathes with very heavy tailstocks equipped with a system for racking the tailstock roughly into position before using the tailstock quill for more finely controlled movement. On some very large machines, the rack movements may even be motorised.

LEADSCREW:
The leadscrew is usually coupled to a set of gears (often in a gearbox mounted in front of the headstock) that allows the leadscrew to rotate in a fixed ratio to the rotation of the lathe spindle - the ratio being set by the gear train selected. The apron usually carries a "split nut" mechanism which allows the lathe saddle to be coupled (or un-coupled) with the leadscrew as required. This is how we are able to cut threads and also provides for saddle fine feeds. Professional machines often save wear on the leadscrew by providing a separate saddle drive system.

So the short answer is: rack for quick and dirty movements, leadscrew for slower movements in direct ratio with spindle rotation.

Don't underestimate the potential of the handwheel-operated rack feed system. I have been able to produce balls of adequate quality when the quantities and time available did not warrant making a dedicated ball-turning attachment, by roughing out with combined cross- and rack feed and finishing with a file followed with an emery polish.

I hope this helps you.

[suther51]

Thank you for the reply. I likely did not articulate my question well, what confuses me is the ability to select power to the rack instead of the lead screw by flipping a lever on the apron. Powering the carriage with the lead screw makes scenes to me for accuracy. But when the rack is powered through the gear box the motion is jumpy and inconsistent. This all makes me wonder why some thing more than hand power on the rack might be needed. Thanks
Eric

[Papa Smurf]

Hi Eric,

I'm going to have to make a few educated guesses based on general practice, since I do not know the specifics of your machine, and I live in Germiston (part of the Greater Johannesburg metropolis), South Africa so I can't just "pop by".

In order for your saddle or carriage to move under power other than from the leadscrew via the half-nuts, a number of different systems were used, the most common of which were:
1. An additional shaft that runs parallel to the leadscrew rotates to transfer driving power through the saddle gears to the pinion which engages the rack, or
2. The leadscrew has a keyway along its length, and driving power is transferred through the saddle gears to the pinion which engages the rack.
These systems were intended to reduce the wear on the leadscrew when screwcutting was not required, since the leadscrew was originally made to fine tolerances to ensure consistently accurate threads. Depending on the complexity of the gear system in the saddle, a powered crossfeed was also possible. An interlock mechanism was necessary to prevent simultaneous engagement of the leadscrew and the rack-driven system - this is probably the lever you mention.

Your description: "when the rack is powered through the gear box the motion is jumpy and inconsistent" leads me to think that there is significant (= excessive) wear in that entire power train. Gear systems that are in good condition don't move in a jumpy and inconsistent manner. You can do basic troubleshooting by moving the carriage all the way to the tailstock end, where the rack would have had the least use, so you can assess the amount of wear on the pinion itself, as well as getting an idea of the wear in the bushes and other gears in the saddle system. You may have access to one of the USB "snake" cameras or endoscopes to help you see inside the saddle without taking it apart. Another indicator of whether the problem is isolated or throughout the rest of the machine is where was it used for most of its life - I wouldn't touch a machine that worked in a foundry, because dust mixed with lubricants makes grinding paste.

Ultimately, if you want to make any meaningful improvement, you will have to take it apart. My best advice in that case is find a friend who can help you, preferrably someone who has experience in the maintenance and repair of machinery, and access to some of the tools you'll need while your machine is out of commission.

Nothing is impossible, given enough money, time and patience, but you also need to assess your own motivations, and regularly re-evaluate them. If what is required is not worth the time, effort and money needed, cut your losses.

Hope this helps,
Russell (Papa Smurf)

[Toolmaker51]

Papa Smurf's descriptions are accurate. The 'lead screw', gear rack, 'feed rod' are as described, and each performs a distinct function.
Some lathes may have 1 or 2 more. One popular feature is a manually operated rod with stops or cams which trip a 'kick-out' for carriage travel.
Another rod, usually on long beds or heavier lathes with a motor & clutch arrangement to engage the spindle, some will even reverse. One is near headstock and bed, other travels with the carriage. Not only a safety feature, saves steps as well.
Import machinery tends to mimic and mix features their designer sees as worthy (if not dropped by accountants or marketing), that usually not had occurred in old iron. The imports realize this and put effort into what they want to sell; certainly some less successfully than others.

In years gone, a mix of features were geared to attract certain types and sizes of work shops. Most older businesses I've worked for, you'd see certain brands selected carefully, to take advantage of selling points. Those impressions bred preferences, and every thought used in assembling my shop too. Maybe I'd run 30+ different lathes, 20+ mills, who knows how many grinders....large or small. Like others, those experiences might become nostalgic, but rarely impulsive purchases.

[suther51]

Again I thank both of you for the responses. As this lathe is new to me and my memory is a bit questionable at times your comments and explanations have helped with my recall of my experimenting with the lathe. One lever on the carriage switches between the cross slide and the lead screw. If the cross slide is selected then a second lever alows the choice of power to be sent to the rack. Saving wear on the lead screw was one of the things I considered but I prefer not to make too many assumptions. While I may never do much more than farm equipment type repair with this machine I would like to be informed to a higher level. Thank you for the help, I shall tell both my father and my uncle of the reason for the power rack option. Unfortunately I may never learn enough due to lack of time to out grow this beat up lathe but I'm still ahead of those who may never run one at all. Thank you both
Eric

[Toolmaker51]

That you own a machine puts you ahead of an unfortunately large crowd.
Even without a machine tool, just being interested is still beyond that crowd.
That's what autodidact learning is all about, you learn by exposure and experimentation.

[owen moore]

The gear rack is only used when you are turning the hand wheel on the side of the apron to traverse the entire carriage assembly manually.

[suther51]

The gear rack is only used when you are turning the hand wheel on the side of the apron to traverse the entire carriage assembly manually.

Thank you for the response
What had puzzled me was that there is the option to select power to the leadscrew or to the rack, two ways to move the apron under power. From the earlier replies it seems that the powered rack option is to save wear n tear on the leadscrew when not threading. Understandable but seemed a bit redundant. Happy building n doing
Eric