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• ## Re: [penturners] Lathe Speed Question??

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• Randy, I have a Jet, JWL1236 lathe. (I believe it is considered in the Midi range) It has the Variable Speed set-up I believe is called the Reeves style.
Message 1 of 6 , Dec 1 4:43 AM
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Randy, I have a Jet, JWL1236 lathe. (I believe it is considered in the
"Midi" range) It has the Variable Speed set-up I believe is called the
"Reeves" style. ( 2 variable, spring loaded pulleys.)
I would imagine that the differing speeds are merely set up at
increments that happened to be handy for spacing the "Stop" notches for the lever.
Figuring the exact place to place the Stop points to attain specific speeds would
be challenging for even the best mathmetician/engineer, then, there is the
additional disadvantage of having to place them that precisely in a casting
mold. ( The main portion of the Head-Stock is Cast Iron.)
Think this way, "It is easier to make it, then determine what speed it
is than to determine what speed we want, then make it to those specs."
For the bottom line, speculatively, most likely a matter of
convienience, For The Makers. lol
Yeah, I am somewhat "Cynical" concerning most "Big Business" in my
beliefs that they are mainly concerned with their convieniences over customer
convienience.

Joe: currentscrafts@...

[Non-text portions of this message have been removed]
• Look at adjacent gear ratio, not difference. You ll see a fairly constant ratio. Remember log scales? ;-) Why? A (linear) change of say 300 RPM from 300
Message 1 of 6 , Dec 1 8:40 AM
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Look at adjacent gear ratio, not difference. You'll see a fairly constant ratio. Remember log scales? ;-)

Why? A (linear) change of say 300 RPM from 300 RPM to 600 RPM doubles the speed, quite noticeable, speeding up by a factor of 2. It's negligible at 3000 RPM - from 3000 to 3300 is only a 10% change, barely noticeable

Why no lower than 500? Ask Jet! They must have figured that was low enough. The lathe has a small swing. Large swing lathes need a lower low end because people want to put a large piece on. No, I imagine they are not terribly concerned with someone using it for a purpose a lathe was not really made for - applying a CA finish.

But I don't speak for Jet :-)

On 12/1/2005 at 6:38 AM zoxxxxoz wrote:

>I'll try some of the experts here. My JET mini will run from 500 RPMs
>to 3975 RPMs in 5 steps. If the speeds were evenly divided, each step
>would be 695 RPMs; but JET didn't evenly space the steps through the
>full speed range. As the machine is set up now, the steps are...from
>LS to HS...340, 400, 560, 830, and 1345 RPMs.
>
>Does anyone "KNOW" why the arrangement is the way it is or care offer
>an opinion/speculation?? Also, any thoughts on why they didn't have a
>lower "low" speed? 500 RPMs seems to be a little fast to me for the
>low end?? Thanks. Randy

--
Regards,
Rich
========================================================
Richard Kleinhenz
penturners moderator
Keep the group tidy! Delete excess text when quoting! Delete fullsize images!
========================================================
• Joe: I have to agree with your comments about manufacturers. It does seem that many times, they are more concerned with their needs than those of the
Message 1 of 6 , Dec 1 1:59 PM
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seem that many times, they are more concerned with their needs than
really don't apply to me because my lathe changes speeds by moving a
belt manually on a stepped pully and not some VS mechanism. Randy
• ... Good point, Rich!! If I had been using my brain, I would have seen that myself. Turns out that the ratios are even more constant than one might think!!! If
Message 1 of 6 , Dec 1 2:47 PM
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--- In penturners@yahoogroups.com, Richard Kleinhenz <rlkl@b...>
wrote:
>
> Look at adjacent gear ratio, not difference. You'll see a fairly
> constant ratio. Remember log scales? ;-)

Good point, Rich!! If I had been using my brain, I would have seen
that myself. Turns out that the ratios are even more constant than
one might think!!! If you look at the speed increases or decreases
as a % of the current speed they are as follows:

Speed
(RPM).............%change....%change
.....(change)....(increase).(decrease)
500
.......340...........68.........40
840
.......400...........48.........32
1240
.......560...........45.........31
1800
.......830...........46.........32
2630
.......1345..........51.........34
3975

It looks to me like the designers were thinking in terms of speed
decreases rather than speed increases and did try to get a slower low
end(note the bigger jump); but it is not obvious why they quit at
500???

Thanks for pointing me in the right direction. Randy
• ... The Jet Mini is pretty much the same as the Jet Midi. The smallest sheave on the pullys is close to the motor shaft size (and the headstock spindle size).
Message 1 of 6 , Dec 1 3:39 PM
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zoxxxxoz wrote:
> --- In penturners@yahoogroups.com, Richard Kleinhenz <rlkl@b...>
> wrote:
>
>>Look at adjacent gear ratio, not difference. You'll see a fairly
>>constant ratio. Remember log scales? ;-)
>
>
> Good point, Rich!! If I had been using my brain, I would have seen
> that myself. Turns out that the ratios are even more constant than
> one might think!!! If you look at the speed increases or decreases
> as a % of the current speed they are as follows:
>
> Speed
> (RPM).............%change....%change
> .....(change)....(increase).(decrease)
> 500
> .......340...........68.........40
> 840
> .......400...........48.........32
> 1240
> .......560...........45.........31
> 1800
> .......830...........46.........32
> 2630
> .......1345..........51.........34
> 3975
>
> It looks to me like the designers were thinking in terms of speed
> decreases rather than speed increases and did try to get a slower low
> end(note the bigger jump); but it is not obvious why they quit at
> 500???
>

The Jet Mini is pretty much the same as the Jet Midi. The smallest sheave on
the pullys is close to the motor shaft size (and the headstock spindle size).
That would limit the small pulley diameter. The Largest sheave on the pulleys
then is the limiting factor - larger diameters would necessitate a larger
headstock - which would interfere with getting in close to the headstock end
of small turnings - my main complaint about my D-1440. The OneWay 2436 on the
otherhand does have a nice small diameter headstock - but that machine is way
overkill for making pens :-)

--
Mike
http://www.ohmywoodness.com
http://mike.vorefamily.net/twr
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