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View Full Version : South Bend/Grizzly lathe change "gears"



DR
03-27-2012, 07:43 PM
I got to look over the 8" x 18" Grizzly machine with the South Bend label.

The interesting thing to me was the way they did the change gear train. Rather than gears they used timing belts and toothed sprockets. The feed reversing tumbler (is that the correct name?) gears were conventional

I've wondered for years why this is not common practice. Probably very quiet running. Might be quicker to change ratios, not having to worry about gear tooth clearance, etc.

Generally, the machine appeared to be a substantial cut above the usual import in construction and quality. Certainly no bargain IMO at around $3500 delivered for a machine with no power cross feed.

aboard_epsilon
03-27-2012, 08:00 PM
That must be the 8k you're talking about, the other one... the 10k has powered cross slide

both are south bend only, as far as i know ..i take a bit of an interest .

the 10k ...well it has three positions on the handle ..and a clutch...so i assume it has power cross slide

all the best.markj

justanengineer
03-27-2012, 09:24 PM
I suspect the belts and sprockets are justified to help minimize damage caused by crashing the machine. In reality, I believe it is done as a cheap manufacturing method.

SGW
03-28-2012, 10:05 AM
Yes, it should be a lot quieter than a train of straight-cut gears. The 8K has a fairly small range of thread pitches it can cut, however. I don't know if that is an inherent limitation of the belt drive setup, or if one could buy additional sizes of toothed pulleys and expand the range of threads.

Interesting that you say, "Generally, the machine appeared to be a substantial cut above the usual import in construction and quality."

That is what the ads claim. It's nice to hear that it may actually be true. At $3300 or whatever it is, is it overpriced? Is its quality worth that much more than a regular Grizzly-brand lathe of similar size? I guess that is up to the buyer.

DR
03-28-2012, 01:23 PM
Yes, it should be a lot quieter than a train of straight-cut gears. The 8K has a fairly small range of thread pitches it can cut, however. I don't know if that is an inherent limitation of the belt drive setup, or if one could buy additional sizes of toothed pulleys and expand the range of threads.

Interesting that you say, "Generally, the machine appeared to be a substantial cut above the usual import in construction and quality."

That is what the ads claim. It's nice to hear that it may actually be true. At $3300 or whatever it is, is it overpriced? Is its quality worth that much more than a regular Grizzly-brand lathe of similar size? I guess that is up to the buyer.

As to the construction and quality....it was little things like the carriage feed hand wheel ran true,without the wobble you see on lesser machines. The end cover hinged door was heavier gage material than it needed, it was well made and the locking mechanism to keep it closed actually lined up (you didn't have to lift and push down on the door to latch it).

The threading chart was one area they cheaped out. It appears to be a glued on piece of heavy paper or plastic. It would have been better to have an embossed metal piece instead. Over time threading charts tend to take a lot of abuse.

The ball oilers were notable, instead of being the common flush-with-the-surface type they stick up a bit. Hard to tell if that was a decorative touch having their brass contrasting with the paint and ground steel/iron surfaces.

Maybe the price actually represents what it costs to build a "special" design machine with low volume in China. I envision the lesser, generic lathes come off high volume production facilities to be profitable, sort of a "on Tuesday we label them Grizzly, on Wednesday they get Jet labels, and those that don't pass our lax quality standards get HF labels".

Whether the cogged belt drive is to minimize damage in the event of a crash, I don't know. Not sure whether the belts would jump teeth or not. The belts were fairly light duty, but still probably strong enough not to break. Cogged driving belts are a well proven technology in machine tools, CNC machines almost exclusively use them. Why it hasn't been done on manual lathe feed gears is what puzzles me.

Arthur.Marks
03-28-2012, 02:08 PM
I'm a sucker for these conversations. So here I go :D

The 8K. As far as cogged tooth belts go, Wabeco has been doing it for decades on lathes of this size. Given the smaller range of threading on those as well, I tend to think the design of the belt possibly limits the available tooth count on the pulleys. Too small and the teeth don't seat or wrap. Too big and the pulley doesn't physically fit. It seems a belt's tooth is probably much larger than a gear tooth. So it becomes a balance. I don't really know, though.

Personally, I find the specs on the 8K to be very pleasing---if perhaps a little too much so ;) I also suspect the higher price is due to the reasons mentioned above but more significantly that the spindle bore is so large. Everyone wants the spindle bore big bigger biggest, but what is lost in the conversation is that the spindle bearings must get larger as well. That can drive cost up real fast, I think. Not only do the bearings have to be larger to physically fit the larger spindle through them---they have to withstand much larger cutting forces. I think we all understand here that the forces involved as you cut larger work do not exactly follow a 1:1 ratio of diameter:forces.

My biggest sore point is the compound design. I don't know why this became "the standard" for these size lathes.:( It just sucks. I owned a Jet 9X20 in my time. All of those have the exact same design. Look, for comparison, at the design of the 10K (the new, sold today 10K). The 8K design is just sooooo less rigid. I still use a similar swing lathe (8") but it uses a compound design much like the 10K's. Even the Wabeco lathes use that inferior design, and I can't understand why. What is the benefit? Two t-slots? I guess if you are doing a lot of line boring that could be useful. The compound can be entirely removed. It would be possible to position the compound anywhere along the entire cross-slide table... but it isn't! :confused: The central rotating pin of the compound has only one position for mounting. Looking back on my newbie experiences with my old 9x20, the weakest link is clearly the lack of rigidity in the compound mounting. The entire rigidity of the lathe hangs on this because even if you never used the compound slide, it always is holding your cutting tool.

IOW... the compound is not physically bolted down. Instead it is sandwiched in place by a "hold down" plate. You must also take into account that this reduces the mounting foot diameter of the actual compound base. The hold down plate must go over it; the compound must have a small diameter cylindrical section to go through it; whereas, the compound itself could be the full diameter of that plate. Next, you loose all that height, again, to accommodate the hold down plate. This drastically reduces the size of the dovetails for the compound slide. I mean, I just don't get it. Bad design, IMO and IME.