Thread: Turret spindle thingy project

Hi Bob, I studied your suggestion for a minute and I reckon I can get that to work. The current setup's main advantage is that it's adjustable by varying the cable length, you raise or lower the foot pedal and change stroke you can get. In the photo I'm using small G clamps to lock the cable at the motor end as I needed to position the motor along the post to suit the belt length. It's not good practise for the bearings to do so, I may move the spindle pulley outboard of the grinder wheels as that would allow an even shorter belt as it doesn't need to clear the wheel when slack. In a perfect world the pulley would be dished out enough to allow the belts to sit right over the bearing and housing.

I ended up needing only half the 40cm+ slide travel for those 55 inch belts as the pedal is below horizontal: once I'm happy it all works and I don't need to increase the belt length, I can modify to your suggestion and maybe change the pivot point to increase the leverage, say 2:1 (40cm pedal to 20 cm motor movement) to lighten the effort of moving a cast iron motor up and down.

Originally Posted by Graziano

Hi Bob, I studied your suggestion for a minute and I reckon I can get that to work. The current setup's main advantage is that it's adjustable by varying the cable length, you raise or lower the foot pedal and change stroke you can get.

You could adjust the extent of the motor lift with my suggestion by changing the centre of rotation of the pedal. To do that, the pedal arm and the arm that is welded to the upright would need a series of co-centric holes drilled along their length and you could just move the rotational axis to the pair of holes that corresponded to the amount of travel you need.

A complete alternative to the pedal is to lift the motor up to its maximum height under the the turret arms and fix it to the column. Then place the spindles on separate rotatable/lockable bases - like I have on my turret. To slacken the belt you would just loosen and rotate the base and spindle slightly. With suitable stops, the bases could be prevented from rotating too far so a loose base would not permit a rotating wheel to strike its turret arm. This arrangement has the advantage that it uses a short belt and is relatively simple.

I still think changing belts will be a nuisance. I just think of the number of times I have to do it on my DP and keep thinking I must put a VSD on that thing.

Originally Posted by BobL

You could adjust the extent of the motor lift with my suggestion by changing the centre of rotation of the pedal. To do that, the pedal arm and the arm that is welded to the upright would need a series of co-centric holes drilled along their length and you could just move the rotational axis to the pair of holes that corresponded to the amount of travel you need.

A complete alternative to the pedal is to lift the motor up to its maximum height under the the turret arms and fix it to the column. Then place the spindles on separate rotatable/lockable bases - like I have on my turret. To slacken the belt you would just loosen and rotate the base and spindle slightly. With suitable stops, the bases could be prevented from rotating too far so a loose base would not permit a rotating wheel to strike its turret arm. This arrangement has the advantage that it uses a short belt and is relatively simple.

I still think changing belts will be a nuisance. I just think of the number of times I have to do it on my DP and keep thinking I must put a VSD on that thing.

Fair suck of the mango Bob, lets not totally rebuild the machine yet! . I'll give it a go as is before doing any serious modifications: I expect some technical problems like vibration or belt flap but if the layout or setup really bothers me I'll make the necessary changes .

So no takers for "as cast" aluminium spindle castings of any kind?......fair enuff.

Originally Posted by Graziano

Fair suck of the mango Bob, lets not totally rebuild the machine yet! . I'll give it a go as is before doing any serious modifications: I expect some technical problems like vibration or belt flap but if the layout or setup really bothers me I'll make the necessary changes .

Sorry mate, it's just that ideas come into my head far faster than I can execute them

I'll be interested to see how the final Mark I version works and what sort of column lock you come up with.

Cheers

Hi Graziano,
Coming along(unlike most of my jobs lol)
Have you thought about some sort of pin behind the motor pulley to stop the belts falling off while you are changing spindles?


Stuart

Originally Posted by Stustoys

Hi Graziano,
Coming along(unlike most of my jobs lol)
Have you thought about some sort of pin behind the motor pulley to stop the belts falling off while you are changing spindles?


Stuart

Hi Stu, I had been thinking of a couple of discs either side of the pulley that are larger in diameter if it became a problem, I've played around with pulling the belts off and on the pulleys one-handed and it's pretty straightforward: you just hold the belts in your right hand and plonk them on the top of motor pulley and pull them towards you until they are tight, then over the 250mm silicon carbide grinder wheel and on the spindle pulley. As you take your foot off the pedal the pulley grooves are enough to guide them until tight.

A problem I have identified is getting the belt off if there is a grinder tool rest and wheel guard fitted: I easily can fix this if I have the spindle pulley on the outside of the grinder wheel. The alternative is a tool rest that slides sideways to clear the wheel. I guess it all comes down to this: is it better the have the grinder wheel closer to the spindle bearing or to have the pulley closer to the bearing?. The shaft is the recommended 20 mm diameter according to the Norton grinder wheel handbook.

Had an interesting development today when I went for a walk: there's an unused stretch of road nearby that local arseholes use for a garbage dump. I spotted a fold up pram and an exercise machine dumped there today (I wonder what story they told: an ex boyfriend/husband dumped it?). Anyway I knew that exercise machines have a decent sized permanent magnet motor usually and this one had a 1.75Hp continuous rated motor. Now the motor is rated at 100 to 130 Volts D.C.......normally this would be a problem except for the fact that I design and manufacture 240 Volt AC to 180 Volt DC motor speed controllers as part of my daily bread . A while ago I'd built a prototype 240 to 180 Volt pulse width modulator controller with a 60 Amp peak capacity for a job that never came through, so I have the prototype lying around for that rainy day, i.e. today. The only problem is the motor is air cooled with a fan drawing air through the motor, so a remote ducted intake would be needed to prevent grinding dust intake.

This is a compact, low profile motor and with a speed controller I can rev it from say 60 R.P.M. to at least 50% over speed. This will be perfect for buffing at low RPM or a higher speed for small diameter diamond wheels and it's rated at 1.75Hp continuous.

Well you clearly have much better " local arseholes" than we do around here.

What a great score but as you say I don't think it will last without an external air supply.

There's not much to show for it photo-wise but I've been making some progress on the Hexagruff/Spurret. It's now set up to run one spindle via the AC motor mounted below, I think I'll hold off on the DC motor for now until the MkII unit gets made. I capped off the top of the steel post with some 12mm steel so as to have a rigid base to attach the turret locking mechanism which is also made from 12mm steel ( I get laser offcuts cheaply ). At present I can rotate one arm into position and then use a small G clamp to lock the hub from rotating.

So far it's all going to work fine, though some things have come to light: the turret part needs to be accurately made in terms of angles of the channels relative to each other and the angle off horizontal. I cut the angles using a small engineer's protractor to mark out then cut freehand with an angle grinder. If I'd spent more time than I did jigging and tacking the channels at uniform angles from horizontal and vertical it would save aligning and mounting of the spindles later on: even a small error of a degree or so can make a difference. To align the stub axle that the turret spins on I had to cut the column and reweld with a slight lean forward to bring each of the three arms closer to level when swung into position. If/when I do it all over again, I'll make the three armed turret first and assemble it with the stub axle then tack weld into the correct position for final welding.

The sliding motor mount isn't rigid enough on it's own and I need to use a couple of timber wedges to lock it into position so the pulleys stay in alignment, while I can't ensure the motor and the spindle shaft are parallel to each other, I can get the pulleys in the same plane of alignment though there could be a slight "twist" relative to each other. The motor is going to get a new hinged mount now that I know where it needs to be and how much it needs to move. It should be possible to use the other side of the pivot point to pull the spring loaded turret locking pin with a short rigid arm or cable.

I do notice the motor has it's shaft centre drilled and accessible and I reckon I can make a simple alignment jig to clamp on to the motor centres at one end and clamp on to the spindle centres at the other end. This would allow me to drill each of the four spindle mounting holes with the spindle locked parallel to the motor.

The one spindle I have fitted runs with some vibration as the wheels aren't trued yet, the vibrations damp down a lot at the stub axle hub which is so stiff and rigid it readily transmits vibration to the column. At the spindle end of the arm a glass of water jump off from vibration, at the stub axle end of the arm it just sits there with a ripple. The belts have about a 2 cm flap every few seconds on some harmonic interval, I'm hoping the hinged motor mount combined with a tension spring or gas strut to get belt tension will dampen vibrations further than the current setup with the motor wedged to the column........phew!

Incredible , very Leonardo da Vinci in flavour.

Originally Posted by Retromilling

Incredible , very Leonardo da Vinci in flavour.

Heh, over the years things I've done have been compared with a lot of other things.......but this is the first time it's been Leonardo Da Vinci . There has been some earlier tri-grinder units including Bobl's version with three bench grinders.

Hi Graziano,
Perhaps fix the motor to the column and use another pulley to tension the belts?

Stuart

Originally Posted by Stustoys

Hi Graziano,
Perhaps fix the motor to the column and use another pulley to tension the belts?

Stuart

NNNnnnyyyyeahhhmaybe, I need to make a lot of slack on the belts to get them over the grinder wheel and threading them over three pulleys instead of two could be harder to do. Even longer belts would be needed too.

If the hinge pivot is about 90 degrees above an imaginary line drawn from the spindle shaft to the motor shaft the motor should swing towards the spindle the absolute minimum 20 cm required. The motor would also be able to swing towards the spindle against springs if the belt tension varies a bit, the motor wedges I use at the moment couple the belt vibration to the column.

You know Stu, I am just implementing your motor mount suggestion from post No.11