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Doc Nickel
01-12-2016, 06:36 PM
Two quick questions on the subject of Logan lathe headstocks:

One, anyone know of a good how-to writeup on how to disassemble the headstock? Or barring that, a good exploded view that doesn't look like it's been fed through a fax machine about six times? :)

And two, I'm seriously considering updating my head to an automotive-style poly-vee belt. The flat belt just can't take the HP I need for some heavy cuts- it's a turret lathe, and occasionally I'll use an insertable spade drill or a box tool, both of which can take a pretty fair bite.

I'm contemplating just removing the spindle and underdrive pulleys, surfacing the crowned flat-belt faces down to, well, flat, and then grooving them for the poly-vee belts.

So the question is, would anyone happen to know how thick the pulley is? I found one undimensioned cutaway drawing that suggests the pulley is actually a fairly thin casting, but I'm not entirely sure it's for my model, or even for a Logan. There's another, however, that shows it as specifically being for a Logan model 00, and shows the cone pulley as being nice and thick.

Of course, I can find out once I take the headstock apart, but I'd like to do a little preparation beforehand.

Doc.

jmm03
01-12-2016, 07:33 PM
What model Doc? This place has parts and manuals,although quite proud of them. I am familiar with the 6500 series somewhat,but I never had the headstock and spindle apart.
http://www.loganact.com/
P.S. great work on your equipment, I have been following your lathe rebuild for awhile,very informative, you set a high standard. Hope this helps, Regards, Jim

J Tiers
01-12-2016, 07:46 PM
Do you have the manual? It's available from Logan for something like $25. Repro quality is considerably better than what you describe, at least on mine.

The manual for my model 200 suggests that the pulley is pretty thick, solid from surface to bore in the middle step area. That makes sense, because it has a bearing against the spindle for back gear. I assume you want to avoid using back gear as it is not fast to switch, not turret compatible.

My testing suggests that a rubber flat belt of max width will carry between 35 and 50 lb tension before it slips, based on tests using the middle step. The poly V might double that, I don't know how much better it gets.

While you can get better than what I found, you start getting into some serious belt tensions. The belt I used for the tests is a rubber faced belt that is seriously grippy, with the rubber applied around and into a canvas core, maybe 2 or 3 ply. Comparable to a poly-v in material, or better. But, of coutrse, flat, not actually poly-V.

You do not say what rpm you want. Any flat belt does better power-wise at a higher rpm, or with a larger pulley. belt tension and belt speed are where it is at. Can you put it on the middle or largest spindle pulley and adjust motor speed with the VFD?

You also didn't comment on work size. The Logans were really meant for work that goes thru the spindle (as is any turret machine other than a regular chucker).

Depending on what you are using now, you might try a poly-V without bothering to re-work the pulley, first. You might do pretty well.

janvanruth
01-12-2016, 07:50 PM
just changing to multi v without doing anything with the crowns gave me way more traction

Duffy
01-12-2016, 08:14 PM
I have an 820 and I did as janvanruth did- used an automotive polyvee belt. It works a LOT better than flat leather, and mine was NEW(ish) flat leather with belt dressing! I really do not think that it is necessary to machine off the crowns.

firbikrhd1
01-12-2016, 08:24 PM
The spindle varies with Model so you need to post what model before anyone can help with disassembly and order of parts.
With regard to the Poly V belt, I have always wondered whether it would be worthwhile to flatten the crowns and machine "V"s into the pulleys so the belt could be run as designed.

Doc Nickel
01-13-2016, 07:02 AM
Actually, I'm not precisely sure what model I have. It was bought (by the previous owner) from an eBay auction some 15 years ago, already set up as a turret lathe.

The quickchange box calls it a Model 955, which according to Logan means it had a standard tailstock and a pedestal mount. The tailstock could have been changed, of course, but this one's set up on a cabinet. In any case, 955 should be close enough- all the other specs are the same. (2-1/4"-8 thread, 24" centers, 1-3/8" bore, flat belt, etc.

Yes, I'm aware that I could use just the poly-vee belt as is, without cutting the cone. And I may still try that. The belt that's on it now is a rubber/fiber composite, not leather or canvas. And for most work it's fine, but if I try to take a heavy cut (admittedly probably heavier than it was ever intended for) it "pops off"- sliding off one pulley or the other.

But designed for it or not, I do use this for short-run production, and in a couple of cases, like using a spade drill, I have to take a certain amount of bite. I can limp things along on the current belt with some belt dressing, but I have to keep reapplying it every couple dozen parts.

I'm not yet 100% convinced I'm going to switch belts though, considering I either have to cut and sew the belt, or will have to machine slots in the bed casting. (Seriously, whose idea was it to have the belt wrap around no fewer than three non-removeable parts?)

Doc.

J Tiers
01-13-2016, 10:41 AM
Do you have that running on 3 phase or single phase?

I used to have that slide off problem, but once I put in 3 phase it pretty much disappeared. That "pulsing". of single phase seems to break the belt loose to slide really easily. Three phase has a constant power flow, no pulsing. Stopped belt pop-off immediately.

Obviously oil on the belt really causes trouble with slipping. You knew that though.

flylo
01-13-2016, 10:51 AM
I haven't tried it but in the deal I got 2 Logans & 2 Warner Swassey's, 1 each with collet closer & a turret & double cut tool post & the other 2 with chucks & tailstocks. The turret is a single lever. Kind of neat seems like he had a large & small machine for most purposes.

Seastar
01-13-2016, 11:03 AM
I have two Logan 200s (it's a long story) and I keep one set up with a three jaw and the other with a four jaw or collets.
The one with the three jaw had a broken back gear when I bought it and I replaced the flat belt with a new one when I replaced the back gear. It's been running for 15 years now without difficulty.
The belt came from Logan as did the back gear.
The lathe with the 4 jaw had a worn out flat belt when I got it. It was probably the original.
I remembered how difficult the disassembly was on the other lathe and replaced the belt with a poly-V.
I can't see any difference in how the two belts perform. Both are on single phase and not on VFDs.
I have never had either slip or jump off the pully.
The flat belt has jumped on occasion if I didn't get it completely on the proper pully but that was on start up.
As I vaguely remember the pulleys are thin castings on this model.
I would not attempt to groove them.
As I remember, JT also has a Logan 200 and he has replaced the headstock bearings.
He probably knows much more than me.
Bill

Sunset Machine
01-13-2016, 12:44 PM
I had to replace a couple of old leather belts on a mill and planer. I took measurements and headed to a belt shop where they suggested different belt materials for each belt. Soon after, I became disgusted with myself for waiting so long. They worked great - much better than leather.

Popping off the pulley - tension problem? Too tight because it slips? Belt stretched on one side? I'd replace the belt before hacking at the pulley - you just know it's not thick enough and probably not enough room to shrink/loctite a grooved ring... Try flipping the belt. If it's stretched on one side that might just "fix" it.

eeler1
01-13-2016, 01:09 PM
Belts sliding off can also be an alignment issue too. Never heard of the 1phase-2phase issue before, but thats a good tip to follow up. Wish I'd heard that years ago!! Exhaust your options before you flatten the cone pulley.

Doc Nickel
01-13-2016, 04:50 PM
Alignment is damn near perfect. Belt is not reversible- it's a rubber composite on one side, a slick backing composite on the other. Flipping it would make the issue worse. I can't honestly say if it's a tension issue since I have no specs- it's "that seems about right". :)

Really, the machine works fine- I'm quite happy with it- for 95% of my work. For most parts, I have no slippage, plenty of power, no tracking issues, no tension issues.

It's only when I really start to push a cut- in this case, a roughly 3/4" insertable spade drill into 1" stainless- that I just don't have the power. I have to put it into back gear for the torque multiplication, because without it, it bogs down- and that's a 2HP Baldor 3-phase motor. If I do this poly-vee mod, I was considering putting in a 3HP.

But that makes me start to worry about the backgear drive pin and key on the spindle. As I said, I'm probably already putting more power into this than than it was designed for.

Doc.

firbikrhd1
01-13-2016, 05:13 PM
It may be that the problem you are experiencing is that you are pushing a machine designed back in the 1950s (or before) to run with 1950s technology (HSS tooling Stellite tooling etc.) harder than it was designed to be pushed hoping to get the full performance out of modern carbide inserts. I'm not saying it can't be done, however a gear driven headstock wouldn't have any issues with what you are attempting.
That said, maybe your headstock could be modified to accept a toothed (cogged) belt type drive which would like stall the motor before slipping. On the other hand, what is the next weakest part in the drive train? Will it go next? Maybe the belt slipping or coming off the pulleys is acting as a safety device for the machine.

firbikrhd1
01-13-2016, 05:13 PM
Double Post

J Tiers
01-13-2016, 08:01 PM
I don't know that you are really stressing the machine. Think of a cut in a max diameter part. I've done that, and it definitely is working the machine, and even with the composite belt, it slips. The power through any flat belt is not likely to break things.

As for carbide, carbide as a cutter material goes back almost to the turn of last century. It is in no way a 50's development, and was commercially available in the 1920s.

The Logan really can't even overwork HSS, since it all depends on DOC and SFM, there are cuts with HSS that are impossible on the Logan, but easy on a big Monarch. It's purely power and thus a volume of removed material per minute issue. Yes, there will be many cuts that a small lathe is just not made to do. If you really want to do them, find a Gisholt and move up.

The real issue of carbide and any small lathe is that you CAN double or triple the SFM with carbide, but the power limits in the small machine drive just don't let you get there. And the fact that carbide is never sharp. In fact, most recommendations from a few years back include deliberately putting a 3 or 4 thou bevel on the edge, intentionally dulling it to get better tool life. It's intended (in those applications) to be crammed-in to the work and take off a big bite at a high SFM. Not gonna happen.

That said, I'd not worry too much about the drive pin. Not with only a 3/4" drill in small stainless. The drive pin is out near the OD of the bull gear, with a significant lever arm advantage against the drill. And, it is not even in the picture when you are in back gear.

Some questions:

Are your pulleys rough or smooth and nearly polished?

Is the rubber surface of the belt smooth, soft, and grippy, or is it rough and hard?

While many folks will indignantly disagree, I find the best power transmission occurs with smooth and almost polished pulleys, along with a smooth, soft, and very grippy rubber. My favorite example of this is your hand against round polished metal. When your hand is slightly damp, not at all wet, but at a certain stage of dampness, that polished metal post will just about tear your skin off, it adheres and grabs so well.

That is what a pulley should do. It's not just "friction", there is an element of adhesion that is past a straight friction situation.

Doc Nickel
01-13-2016, 09:22 PM
It may be that the problem you are experiencing is that you are pushing a machine designed back in the 1950s (or before) to run with 1950s technology (HSS tooling Stellite tooling etc.) harder than it was designed to be pushed hoping to get the full performance out of modern carbide inserts.

-That is precisely what I'm doing. :D


That said, maybe your headstock could be modified to accept a toothed (cogged) belt type drive which would like stall the motor before slipping.

-I'd considered that, but conventional wisdom says the "cogging" will translate into the surface finish. The effect is faint, but supposedly consistent and noticeable.


On the other hand, what is the next weakest part in the drive train? Will it go next?

-Entirely possible. As I understand it, the cone pulley is only connected to the spindle through a pin to the bull gear, and the bull gear only by a key to the spindle. I do not know the HP capacity of either the key nor the pin, and as I noted above, I am in fact worried about that.

Could I put a second pin in? Could I put a second key in? Would they be necessary?

In one of the HSM magazines a few years ago, somebody had an article about making all-new poly-vee belts for an older Southbend, and he made them from aluminum bar stock. Could I do the same thing, and basically delete the back-gear entirely? Have a longer key on the spindle, or multiple keys- say one at the front and one at the back?

I don't know. That's why I'm asking these questions. :)


Maybe the belt slipping or coming off the pulleys is acting as a safety device for the machine.

-And it has. The slippage has saved me from a couple of minor crashes on both my smaller lathes. And I'm worried about such a crash on my new (to me) bigger gearhead. It's been a long time since I crashed something (many years) but a slippy belt on a 2HP machine is different from a 10HP gearhead with shafts and gears the size of a heavy truck transmission. :)

Doc.

Doc Nickel
01-13-2016, 09:42 PM
I don't know that you are really stressing the machine.

-I don't know either. For example, I know that the stock Logan underdrive uses a standard A-series v-belt off the motor to the conehead jackshaft, but the factory pulley on the shaft has no groove. The power is transmitted simply through the flat base of the V-belt.

That belt has never given me a lick of problem, or the slightest hint it's slipping. If I beef up the headstock drive, will that belt, then, become my "safety valve"?


Yes, there will be many cuts that a small lathe is just not made to do. If you really want to do them, find a Gisholt and move up.

-I agree, but not always a choice. I'd love to have something with a lot more inherent strength but not that much larger a footprint, like a Monarch 10EE. But I'm in Alaska, and machine tools in general are rare, rare tools (like a 10EE or HVL-H) go for an even greater premium than you fellows in the States pay, and shipping anything up costs a fortune.

I know where I can get a big Jones & Lamson turret lathe... except it weighs 20,000 pounds and requires its' own hydroelectric dam to operate. :) My big Springfield, a 10HP gearhead, should have plenty of power, but it's poorly laid out for coolant (at least soluble) has no turret and I have no collet system for it. I could work around most of that (mostly by throwing a bunch of money at it) but that's not really what I wanted.


Are your pulleys rough or smooth and nearly polished?

-Pretty smooth.


Is the rubber surface of the belt smooth, soft, and grippy, or is it rough and hard?

-Also smooth.

As I noted earlier, adding belt dressing helps immensely, but it doesn't last. It's not a huge hassle when I'm only running 20 or 30 parts, but it starts being a problem when I have to run 200-300, and reapply the dressing every 10-20 parts.

Ideally I'd like to have the traction to not need the dressing at all, and possibly bump up to a 3HP motor.

Doc.

J Tiers
01-13-2016, 09:54 PM
My drive belt is smooth enough to be just short of glossy. It's not at all dull, more like a glossy surface that just isn't actually quite glossy.

And I polished up the pulleys but not quite to the stage of "shave in the reflection".

My father in law has an old Southbend 9" with an ancient leather belt on it, that was old when I first saw it in 1984. The pulleys ARE basically "shave in it" smooth, and the belt has a glossy surface on the contact side. That darn thing has power out the wazoo, and torque that won't quit.... ON SINGLE PHASE. The belt grabs that polished pulley like nobody's business.

I have never seen him stall it, and he works it pretty hard. And for sure the belt never slips off the pulleys. heck, it never slips period. It's something to do with the grip of the belt on the surface, for sure.

The only belt dressing he uses is neat's foot oil to keep the belt pliable and soft-surfaced. The sticky compounds don't last.