Long Beds vs Short Beds

[TurningDog]

In my quest to make a better cheaper bigger lathe I met a most helpful ally, an engineering grad student in need of a project who has a passing interest in woodturning 🙂

The quandry we keep running into is should we go short bed with a boltable extension, this keeps the costs down if we put it into production for buyers who have no plans of making anything but bowls. However as a turner with a short bed mini lathe I bought the extension just to keep from having to take my tail stock on and off every time it got in the way. As turners would you rather pay more (several hundred most likely) for a long bed, pay a few hundred more to get an extension or just take the tailstock off and set it aside when not in use. Mind you the tail stock is nearly 100 pounds of cast iron.

 

[Mark Mandell]

Bo'fum

Meaning a sl-i-i-i-i-ding bed. Looked at a Stubby lately? I have a shortbed lathe for footprint and access to the headstock, yet I can turn up to 34" without sweating an extension. Haven;t had to sit on the bed even once. 😉

m

 

[Bill Boehme]

Neither -- but, this instead

Neither one. Not that I am planning to buy a lathe anytime in the foreseeable future, but I would be much more interested in a long bed lathe (like 35 inches) with a movable headstock (with a swing of around 20 inches). That would address the question without the need to buy something else. And it would be nice to have the option of attaching an extension of about 18 inches.

Tailstocks are heavy, but is 100 pounds really necessary? You could save some money by strategically removing metal where it doesn't add anything to mechanical stiffness.

Although marketing it may be just a distant thought right now, think about features that would be discriminators to clearly distinguish it from other lathes on the market. Without that as part of your business plan, it would become just another "also ran".

Bill

 

[TurningDog]

I will have to have a look at the stubby. Our design is similar to the Ray Peck bowl lathe and will allow the bed in 2 positions high and low one giving 24" the other 46"

 

[MichaelMouse]

The two most pretentious sayings in woodturning:
"Buy your last lathe first" & "You can always turn small things on a big lathe, but not big things on a small lathe"


Add a third. You can turn short things on a long lathe, but not long things on a short lathe.

Depending on how you turn, it really doesn't make squat if the headstock moves to the end. Not sure that there's much call for round things over 20" in diameter anyway.

 

[Mark Mandell]

Not sure that there's much call for round things over 20" in diameter anyway.

Well, I can tell you there are two resturants near me that love the show they throw with their 26" maple and cherry salad bowls (waiters can get a 18-20" toss without spilling a drop) and have orders in for 4 "large" in walnut with stands. [I have the tree all picked out]

 

[Bill Boehme]

Depending on how you turn, it really doesn't make squat if the headstock moves to the end. Not sure that there's much call for round things over 20" in diameter anyway.

Two reasons that I like a movable headstock (nothing to do with turning something larger than 20 inches diameter):

1. In a crowded workshop (that would be mine), it is frequently more convenient to move the headstock closer to the tailstock end so that I don't have to try maneuvering across the bed of the lathe. Moving the headstock give me more unobstructed room to waltz.
2. The lathe is usually more stable when I move the headstock closer to the center of the lathe when I have a large heavy piece of wood mounted that I am roughing out. It distributes the weight more evenly among the four feet and makes it less likely to rear up on its hind legs and then gallop across the shop.

I agree about hardly ever needing anything with a swing over 20 inches. I have never turned anything over about twelve inches or so. However, other people do. Some members of my woodturning club routinely turn large objects.

Bill

 

[Claude]

There is a third solution to your dilemma.
If you take, for example, the Vicmarc 300, it comes either with short or long bed. The tail stock is very heavy, and you need to be Schwarzenegger or very young to be able to put it on and off.
The solution has been developed by Vermec and is constituted by a very small extension where you put the tail stock, and then you open away this extension. Real convenient.
Now if you speak about a small lathe (which I call bench lathe) most of the time the extension is exclusively used to put the tail stock away. Rarely does someone turn a 20 cm diameter, 1 meter length piece of wood on such lathes.

 

[hcbph]

I think you need to figure out what your audience is first. If it's for bowls, then probably a short bed would work. If it's spindle turning then longer is better. Happens I do spindle type turning (legs, spindles, etc) so when I got my Jet 1642, I also added a 18" bed extension. Now I can turn up to 60" just fine.
Here's a thought, why not all of your ideas? Using the Jet as an example, you have the headstock and tail stock that can slide off the bed. Have a shortbed option, a long bed option and a bed extension option. Take the headstock, tailstock and bed length of your choice when ordering.
If the internals were heavy enough to handle the load, add riser blocks to increase the swing of the lathe. That could really make an adjustable lathe.
Just a thought.

Paul

 

[TurningDog]

Have a shortbed option, a long bed option and a bed extension option. Take the headstock, tailstock and bed length of your choice when ordering.


If the internals were heavy enough to handle the load, add riser blocks to increase the swing of the lathe. That could really make an adjustable lathe.
Just a thought.

Paul

The big reason for not having a bunch of be options is cost. We are trying to make the lathe come in at no more than $1500 retail without the motor which would mean cost should be no more 60%. Since we will have to cast at least 5 of these to get a decent rate on the casting we can't have too many options.

As far as riser blocks go, I am still looking at the option of adding them to a griz sliding headstock lathe. I think I could easily add 2 to 4" inch blocks to their 16" lathe if I match it with a suitably slower VFD drive. the minimum speed of 600 rpms is a scary thought considdering the bulk of my turnings are either very wet silver maple or rather punky spalted silver maple. I can see that first piece of 16" spalt go flying through the wall of my shop.

 

[dkulze]

I see lots of problems in trying to bring in a lathe at under $1500. The first of which is that the motor and controllers are a big part of the expense. Most of the higher end lathes these days have variable speed with some type of dynamic braking. When you're working with big pieces, these two features make a big difference. With no motor, and I'm assuming no VS control, you're looking at several hundred bucks to add just those items (someone out there correct me if I'm wrong), which brings you perilously close to the Powermatics and Novas. Nova even handles keeping their cost down by selling the lathe with no attached stand.

Rotating headstock and outboard rest take care of the short bed question (as does sliding headstock).

Drop in and look at the website for Robust lathes. They're the new kids on the block and offer a couple of features that make them stand out including a rotate away tailstock.

Dietrich

 

[Mark Mandell]

As far as riser blocks go, I am still looking at the option of adding them to a griz sliding headstock lathe. I think I could easily add 2 to 4" inch blocks to their 16" lathe if I match it with a suitably slower VFD drive. the minimum speed of 600 rpms is a scary thought considdering the bulk of my turnings are either very wet silver maple or rather punky spalted silver maple. I can see that first piece of 16" spalt go flying through the wall of my shop.

Here's more scary still:

As a turner, you're going to be aware that spinning a 15-19" rough log at 600 rpm is probably, by definition, unreasonably dangerous to the operator unless the lathe is massive and bolted to the floor with an equally massive tailstock in place.

You also know that at your price point you will not be selling anything like 1,500 - 2,000 POUNDS of iron that then gets anchored in concrete with 1" bolts. I'm sure that you can also anticipate that an operator will attempt to mount something big without using that 100lb. tailstock. Therefore, I think you do well to see if you can get an insurance company, based on your design alone, to write a policy with enough insurance (at a price you can afford) to cover you when some poor schlunk novice gets killed or crushed after your machine goes south, north, and west all at the same speed and time right after all the nifty warning stickers telling him not to do that have been peeled off. 😱

Dog, also ask your engineer grad/friend about the angular force multipliers involved (if that's the right term or not, you get the idea) and whether he's willing to bet his personal ranch on his design.

Not to preach, but it's one thing to design a machine for your own use; it's quite another to make something for sale to others. I still remember how a law professor I had summed up a lecture on grossly negligent products liability by saying "You may be free to commit suicide, but you're not free to take me with you."

With the availability of VFD drives, and such today, I'd be very scared about putting out a lathe that big with a minimum speed that high.

Just something to think about.

m

 

[TurningDog]

Here's more scary still:

With the availability of VFD drives, and such today, I'd be very scared about putting out a lathe that big with a minimum speed that high.

Just something to think about.

m

let me clarify I would put a slow vfd drive on any lathe I helped design, I was commentiing on griz's scary setup of a 16" with its minimum 600 rpm. If I bought this lathe I would be putting my own VFD drive setup on it, whether or not I added riser blocks. I know in an outboard mode with the headstock slid down to the middle this griz lathe would handle a 20 to 24" bowl or bigger once I put a VFD on it. I know this because I can easily turn 18" bowl with my HF 34706 matched with my current VFD of course I have it bolted to the floor. My only reasons for bothering to upgrade is the challenge of building one and the fact my current one is showing signs of some abuse early on in my turning career. I am sure if I went out and bought a brand new one and made the same modifcations I have now and not subject it to any great abuse it would last for a significantly longer than the 5 years this one already has. Back to the Griz lathe, 600 rpms is bad enough on some 8 or 9 inch out of balance piece, I can't imagine what kind of idiot I mean engineer thought to match this lathe which is suitably sturdy in of itself with a motor that goes a min 600 rpm.

 

[Mark Mandell]

let me clarify I would put a slow vfd drive on any lathe I helped design, I was commentiing on griz's scary setup of a 16" with its minimum 600 rpm. If I bought this lathe I would be putting my own VFD drive setup on it, whether or not I added riser blocks. I know in an outboard mode with the headstock slid down to the middle this griz lathe would handle a 20 to 24" bowl or bigger once I put a VFD on it. I know this because I can easily turn 18" bowl with my HF 34706 matched with my current VFD of course I have it bolted to the floor. My only reasons for bothering to upgrade is the challenge of building one and the fact my current one is showing signs of some abuse early on in my turning career. I am sure if I went out and bought a brand new one and made the same modifcations I have now and not subject it to any great abuse it would last for a significantly longer than the 5 years this one already has. Back to the Griz lathe, 600 rpms is bad enough on some 8 or 9 inch out of balance piece, I can't imagine what kind of idiot I mean engineer thought to match this lathe which is suitably sturdy in of itself with a motor that goes a min 600 rpm.

Whew! 😉
[Ne-ver mind 😱 ]

 

[dkulze]

Hey Dog,

One of the things that seems to be commented on pretty regularly is that the HF and Griz lathes just aren't built that well. They're plenty strong as far as structurally but the tollerances aren't usually that great and the materials aren't the highest quality of manufacture. I'm guessing that a comparable lathe from a higher end manufacturer (Oneway, Stubby, Robust, Nova, Vicmark, Powermatic, even Jet) would not have suffered damage from "early abuse" in quite the same way. These lathes tend to be more in the "lifetime investment" category and don't tend to wear out in quite the same way, even with serious abuse.

Ya get's what ya pays for.

Dietrich

 

[S. Clark]

Hey Dog,

Ya get's what ya pays for.

Dietrich

Exactly! What I've been reading here is so typical; starting out with a price point and designing to it. There are inherent limitations to this approach.

No one has mentioned the VB. They avoided designing to a price point and came up with an excellent solution. I'm not saying that it is a do everything machine. But it seem clear that cost didn't dictate design. A lot of the difficult problems mentioned have been addressed in their design. And yes, you have to pay big $ to own their solution. But then again, it'll probably be the last lathe you'll ever need to buy.

- Scott

 

[underdog]

But then again, it'll probably be the last lathe you'll ever need to buy. - Scott

Oh! Man!

There you go being pretentious again! Gotta cut that out! 😉

Sorry. couldn't resist... 😀

I'll go back to my corner and shut up now... 😎

 

[Bill Boehme]

I think I could easily add 2 to 4" inch blocks to their 16" lathe if I match it with a suitably slower VFD drive.

I don't want to discourage you from your idea, but I would like to toss in a bit of information about variable frequency drives and the motor that are used for this type of service. The limiting factor on speed is, generally speaking, not a function of VFD limitations, but limitations on the operating range of the motor itself. You can't just pick any off-the-shelf three-phase TEFC motor for inverter duty. As a minimum requirement, they need to have at least F class insulation rating and it is necessary in some cases to use H class insulation rating. When a motor runs slower, it gets less cooling air from the ducted fan mounted on the back end so it will need to be a motor with a considerably higher thermal rating. For heavy-duty applications -- I am assuming that you would want at least 1.5 HP for the motor -- you would need to go to a TEBC motor to provide the necessary cooling air. At the high end of the speed range, iron losses and viscous drag both contribute to excessive motor heating and will be the limiting factor for the maximum speed.

The type of VFD's used for lathe drive systems are what is known as V/Hz (volts per Hertz) and they sometimes also incorporate algorithms to estimate motor speed since they do not incorporate any feedback to directly measure it. This scheme works quite well as long as the torque load is fairly constant (not exactly the case on a lathe so it is a compromise of cost vs. performance), but V/Hz performance begins to falter at motor speeds below about 200 RPM if the load is constant and about 400 RPM for a highly variable torque load. For direct control of motor speed at very low speeds and at very high speeds requires a system having what is known as vector control (not the same as "sensorless vector" on lower cost drives). This is achieved by adding either an optical shaft encoder or a resolver onto the motor and using a drive that is able to use this velocity feedback term to provide precision motor control. Since a drive/controller combination in this class costs $4K and up, this puts it out of consideration for any normal woodturning lathe.

Lathe manufacturers achieve a suitable solution to this problem by using stepped sheaves to drive the spindle. In that way, the motor RPM can be kept high enough to maintain motor cooling without going to a TEBC configuration and, at the same time, allow the VFD to operate in a range that maintains good control on motor speed. Most lathes with VFD drives that you see on the market will have at least two speed ranges.

One final thought is that high-tech is not always wonderful. The dark cloud behind the silver lining is that below the motor's base speed (typically about 1750 RPM), the HP rating of the motor linearly decreases with speed.

Bill

 

[TurningDog]

My1.5 hp vfd is a replacment treadmill motor and I added 2 cooling fans to it I can run it for about 2 hours continuously in the 200 to 600 range before my hands hurt (damned arthritis) and I have to give it a break. I must be doing something right in less than 2 years I have put close to 3500 hours on it and the motor shows no signs of being any worse for wear.