Torque increase on a 7x?

[websterz]

I have seen references to using a smaller timing belt pulley on the motor to increase torque. Has anyone done this mod, and if so, was it a noticeable increase? I started building my ER32 collet chuck today and have had some stalling issues, mainly due to the 3.75" diameter material I am using. Now that I have the metal drive gears and tapered roller bearings I want to squeeze a little more low end OOMPH out of my 7x12. Not being really up on my timing belt lingo I am not sure what to even look for in a smaller pulley. The sites I visited had loads of nice new metal pulleys but they wanted to know stuff like the pitch, hub thickness, etc. Dammit Jim, I'm a machinist, not an engineer!  Can someone hold my hand and get me where I need to be?

[Stilldrillin]

Good Question! 

Me too..... 

David D

[andyf]

There are one or two speed reductionr/torque increase projects shown in the Photos section of the 7x12 minilathe group ( http://groups.yahoo.com/group/7x12minilathe/ ), if you want to join it. Look particularly at the albums "Belt Drive" and "Trevor's Lathe Mods".

Received wisdom from that group is that the timing belt and toothed pulleys may not be to a standard pitch. I'm not sure about that; this page about a speed reducer http://www.mini-lathe.org.uk/torque_gear_replace.shtml implies that it is standard.

Andy

[Jonny]

Change the motor is your best bet.
I have one here in a tool cabinet in larger lathe almost brand new gathering dust, cant do a thing with it probably wants triple the amount of torque to make useable.

[picclock]

Hi
The easiest way is to use an idler shaft, then use a reduction gear to the idler and a further reduction via athe belt drive. I've dove this on mine and can turn 5" dia steel all day long. There are quite a few plans for this type of mod on the 7x12 group.

http://groups.yahoo.com/group/7x12minilathe/messages

I did it differently

http://s917.photobucket.com/albums/ad19/picclock/?action=view&current=DSC02448.jpg

originally so that I could put the end on and have it all fit. I think I put the end back once and now leave it with the gears exposed all the time because it speeds up changing them.

A better way may be to use the reduction gearing off of an old battery powered drill. If you get the right type it will give two geared speeds + it will have a torque limiting ratchet that can be set. with the other gears this will give 4 speeds. If I can ever get hold of a decent scrap battery drill I may well give it a go, just for the extra ratio's. The belt on mine has steel reinforcing and the belt and timing sprockets came from Technobots.

Good luck

picclock

(ps once you have all this torque you will want to ditch the compound for a solid block to improve rigidity)

[John Rudd]

Bottom line on this is change to a bigger motor...

All you are doing is using the exisiting torque developed by the motor  but at a reduced speed...Obvious I know..

Changing to a bigger motor isnt really the best idea either because ultimately the lathe has been sized for a certain size motor, increasing the motor will potentially stress the bed.........

Or am I being pessimistic here?

[modeldozer]

Hi

On changing the pulley ratios have a look at my post, some of the collective has posted the detais there.
http://madmodder.net/index.php?topic=4946.0

Abraham

[picclock]

@ John Rudd

A bigger motor may (or may not) makes things easier but its not so simple. The main problem is that the cutting speeds tend to be the limitation at these sizes. I can easily exceed the recommended cutting speeds for HSS and carbide on 5-6" work, so there really isn't much point in going faster and no point in having a larger motor unless it will work the whole speed range without gear changing. A bigger motor may produce more torque for deeper cuts, but the existing one will do 20-30 thou cut depth on 5"+ steel which is quite good for a non production machine.

Best Regards

picclock 

[andyf]

Picclock, looking at your photo, is the motor in its original orientation with the drive shaft sticking out beyond the headstock? If so,  won't your 3:1 gears reverse the direction of the timing belt and spindle? I know you could simply swap over the forward/reverse labels on the switch, but it seems to be a feature of these DC permanent magnet motors that they only run backwards at about half normal speed.

Andy

[Stilldrillin]

There are one or two speed reductionr/torque increase projects shown in the Photos section of the 7x12 minilathe group ( http://groups.yahoo.com/group/7x12minilathe/ ), if you want to join it. Look particularly at the albums "Belt Drive" and "Trevor's Lathe Mods".

Received wisdom from that group is that the timing belt and toothed pulleys may not be to a standard pitch. I'm not sure about that; this page about a speed reducer http://www.mini-lathe.org.uk/torque_gear_replace.shtml implies that it is standard.

Andy

Andy.
My observation of my Chester's belt..... Marked, 1.5m-70-9.5  ..... 9.5mm wide, 3/16" pitch

My spare, from a little used Warco.... Marked, 1.5  70  ..... 9mm wide, 3/16" pitch

My pulleys are 17t x 31t.

Dunno if this info is of any use at all. But I feel I'm being helpful...... 

David D

[SKIPRAT]

Hi There

I have found an article on the UK mini lathe site about increasing torque on the mini lathe it mentions some pulley sizes and gear ratios.there is a lot of other stuff regarding the mini lathe i hope this will be of use to you .

Cheers Paul

 http://www.mini-lathe.org.uk/torque_gear_replace.shtml
 

[Sorekiwi]

One of the popular modifications for this on the Yahoo sites is a jackshaft arrangement by Ralph Patterson.  There are photographs and drawings here:  http://www.toolsandmods.com/library/ralph_patterson_speed_reducer_1.pdf

In a nutshell the motor is replaced by a jackshaft and another set of the original pulleys (and belt) are used to do another speed reduction.  According to those who have done it, it works well.  I bought another belt and pair of pulleys 3 or 4 years ago, but havent got around to building the rest of the bits.  I never use the high range on my minilathe, so I think its a viable solution.

Another thought is that there have been posts on here about increasing torque on the Sieg mini-mills by substituting a KB motor controller.  I assume that that controller would have a similar effect on the lathe as well?

  but while you are on that website...  Another very useful mod that Ralph Patterson has drawn is the "Fine Feed Modification" which is a modification to the leadscrew gear banjo to allow another pair of gears to drive the leadscrew.  Using another pair of 20/80 gears in the train will give a leadscrew ratio of 1024:1 as opposed to the standard fine feed of 256:1.  With a nice sharp tool and the fine feed engaged I have managed some beautiful finishes with this set-up.

[picclock]

@ Andyf

My lathe is a real Bull, and the speed difference between forward and reverse is minimal. If there had been a large difference it would be caused by the controller,  and simply fixed by swapping the motor leads round. These just plug into the speed controller board so its simple to do.  The motor is a permanent magnet type with no position adjustment for the brushes. I suspect that these are generic parts sold as bi-directional motors.  The motor shaft is extended by about 12mm by an adapter made out of a broken pry bar. It works very well but does tend to be noisy. A quieter solution is to use two belt drives to achieve the desired ratio.

@Sorekiwi
You can see the banjo mod in the link posted in my earlier post (6 posts prior). It makes life a lot easier with fewer adjustments needed to set a given reduction. I now use a home brewed electronic lead screw controller, which gives feeds down to 30 thou per minute so the only time the gears are used is for thread cutting. Because its combined with a cheapo caliper the lathe can be set to do repeated passes with just one touch of the button, and it will turn the required length and then rewind the carriage back to the start ready for the next pass. If I had thought to make the cross slide motorised it would just be a case of setting the length and depth and hitting the button. I made it because turning stuff on large diameter metal is about as interesting as watching grass grow - this way I just set the cross slide depth,  touch the button and  - I should have called it the sanity saver    piccy on :-
http://i917.photobucket.com/albums/ad19/picclock/Cheapo%20Electronic%20Leadscrew/Leadscrewdriver.jpg

Best Regards

picclock