Thread: Spider for AL320G

It might be possible to replace the pulley to a smaller one. You would also have to change the motor pulley to keep the ratio right. By the looks of it 40mm smaller would do it.
You could use the commercial aluminum ones most tool places sell, and machine them to suit while you still have the original pulleys on.
Dave

Thanks Dave

Good idea. Do you know what the technique is of matching the pulley ratios?

Scott

Hi Bidgee, Dave,

Time for dumb question, but how do you set up the spider, do you pass the barrel of the gun through the headstock? Which way, muzzle or breech?

If so then you could always make one that goes inside the spindle, assuming that there is enough room.

As far as the pulley ratio's go, just keep the same relationship between the two pulleys, If the motor is 100 and the other end is 200, then it's 2:1, so dropping the diameter from 200 to 160 means you would want 80 at the motor.

Regards
Ray

If you can why not extend the headstock spindle out past the pulley??

Originally Posted by RayG

how do you set up the spider, do you pass the barrel of the gun through the headstock? Which way, muzzle or breech?

Yes, either way depending on what you are doing.

Originally Posted by RayG

If so then you could always make one that goes inside the spindle, assuming that there is enough room.

Yep, I've thought of that but as you've noted it limits the available dia and how do you secure it?

Thanks for info about the pulley ratios.

Scott

Originally Posted by .RC.

If you can why not extend the headstock spindle out past the pulley??

Currently the pulley partially infringes the OD of the spindle, but not the ID. I'd like to do what you are suggesting so If I swap the pulley out to a smaller dia how would you recommend I do it?

Hi Scott,
Measure them both on the outside then divide the large one with the small one and it will give you the ratio
EG
200/100 = 2 which is 2 to 1 ratio
What is the size of the small pulley now? you have to watch it doesn't get to small for the V belt to go around. There are other belts out there though.
I wouldn't worry about the extension now, make sure you can change the pulleys first. Other wise it will be a wast of your time and effort designing it.
Dave

Well I was actually thinking about putting a bush on the inside.. I don't know what spindle bore you have or what is the maximum size you need to fit a barrel in there...But if you could fit a bush in there and fix it via some cap head screws it might be another alternative... And easily removable..

Fitting smaller pulleys might be the go as well..

Originally Posted by Dave J

What is the size of the small pulley now?

Dave

I'm not sure how you measure pulleys and its not easy with the belt on but best as I can determine its 70mm dia on top of the belt and about 44mm bottom of the V.

Scott

Dont worry about where the belt sits in the pulley ,the pulley may allready have a size marked on it.

If not measure the OD of the 2 pulleys divide large by small thats the ratio of the 2.

Might pay you to measure in imperial as most pulleys are still stamped in it.

If you cant get a driven pulley or drive pulley in a suitable ratio to what you have now I wouldnt worry to much as long as its not a dramatic difference,you will either increase or decrease you spindle speed a little.

Just make sure that you get the right section pulley.

You may even find that your supplier will be able to get the pulleys supplied with the correct bore and keyway for a small additional cost.

Havea look at the blackwoods site to get an idea of whats available,if nothing there try motion industries still part of blackwoods but they might show them on there site.

Retaining the ration between the pulleys probably doesn't really matter that much in reality. If you make the driven pulley slightly smaller whilst leaving the drive pulley the same all that will happen is that the spindle will run slower in all the gears compared to the speeds posted on the machine spec plate.

As an example, assuming for the sake of argument that your current pulleys are 40mm and 80mm (ie 2:1 ratio) and that you reduce the driven pulley to 70mm (ie 1.75:1) then the speeds in each gear would go as follows:

Current Speeds
90, 160, 300, 500, 850, 1600

New Speeds (approx)
80, 140, 260, 440, 750, 1400

You'd just need to take that into consideration when selecting the correct gear for the job. It'd be an easy job to calculate the new speed in each gear based on the current diameter of each pulley and the new diameter of the driven pulley.

That way you don't need to reduce the drive pulley and compromise the belt life. Obviously in either case you'll need to change the belt length or make sure the motor has enough travel to take up the slack.

Hi Scott
Going what the others have said about not worrying to much about the pulley size.
Is the large pulley solid? If so you could machine it down 40mm on the diameter to clear. Do you know any body with another lathe to do it? If not you could modify an old pulley to fit your lathe (even if it is bigger), just to do the job on that one. Local tip scrap yard may have something.
Dave