Pulley Sizes For An X2 Clone Conversion

Having broken my second intermediate gear I'm contemplating a belt drive conversion for my X2 clone. This looks to be a suitable belt: belt but I can't find any specs for pulleys, specifically I want to know the smallest practical. If I drive the spindle direct I reckon I need a reduction ratio of roughly 4:1 to match the existing low gear setting. The spindle pulley is limited to around 80mm pcd so the motor pulley would need to be 20mm pcd to achieve that - seems a bit tight but it is a small cogged belt. Any thoughts?

William.

Poly V will allow you to use much smaller pulleys than a single V.

This is the drive system as supplied on my Coronet  wood turning lathe.  The smallest drive pulley is 22mm OD

Rod

Edit to add pic.

Edited By Roderick Jenkins on 22/06/2020 12:00:41

My motor pulley has OD's of 25 & 35mm and the spindle pulley is 60 & 75mm. The V's are 4mm wide x 3.2mm deep

HTH regards

William, look at the page in your link, there are 3 boxes on the right hand side, "Description", "Technical" and "Reviews". Click on the technical box and it tells you the minimum pulley pcd there. Also you can down load the full Optibelt catalogue from www.optibelt.com  which will give you all the information that you need - as well as a load that you don't!

Edited By Keith Long on 22/06/2020 12:40:35

Poly V pulleys are much easier to make than single V. Especially if you have a DRO set on the lathe but, if you have nothing, a simple bedstop and spacer to set the interval between V s is easily knocked up and works well enough with care.

I find the centre spacing calculation formulae for poly V belts given by major makers, both printed in data books and embedded in websites, much more accurate than the usual single V formulae.

Clive

Hi William,

Soon after buying my X2 clone I went through the phase of design and build my own conversion and in the end bought a kit from this guy in Turkey **LINK**

It was simple to fit and has performed well over the years

There are a couple of photos in my album of it fitted

Thanks, is that on a similar machine? Do you use the low speeds much?

Thanks Keith, staring me in the face of course. Spec looks fine, 20mm on the motor and 80 on the spindle gives me the 4:1 and the 2:1 for the high speed should be easy.

I am keen to make this myself because I'd rather invest time than money and I might learn something along the way.

Clive, I can see that a poly belt might be superior but all the conversions I've seen so far use a basic V. Not sure how machining 5 precisely spaced grooves is easier than one big one, could you expand on that?

William.

Hi

After buying an X2 Mill drill over 10 years ago with 2 speed plastic gears and spring assist on the cutting head. Rebuilt it with Taper roller bearings spindle. Fabricate and fitted Two Speed poly vee belt drive four ribs "J' section. Sold off the motor and controller and replaced with a 1.25 hp DC motor with a AC to DC variable speed Minarik Regenerative Quadrant 4 Drive Controller. Ditched the spring assist for an air spring mounted inside the column with adjustable yoke assembly to get maximum travel of the spindle. Now it is hard to recognise as an X 2 mill both in looks and performance. It is not pretty but is practical.

Crikey, there should be a separate thread for most radical X2. Looks as if you've addressed the terrible fine feed as well, does the spur on top of the spindle pulley drive a powered feed?

Have a look at timing belts and pulleys. The pulleys are available down to 10 tooth. I used a pair for my cnc conversion of an SX2P to enable me to move the motor closer to the spindle and give room for the z-axis drive. No problems with it.

Russell

Hi William

"does the spur on top of the spindle pulley drive a powered feed?" No it is a slotted disc used to generate a pulsed signal to an ABS Brakes Sensor off off a Volvo to the Rev Counter off a Diesel Engine with a 96 tooth camshaft gear.

Eric

The poly vee belt grooves are sufficiently small that you can just go straight in with a tool of the correct shape. Think thread cutting without the traverse along the bed.

Even without a DRO precise spacing is easy with a simple spacer the same thickness as the inter groove spacing and something to clamp on the bed to define the saddle position. If you have a simple block type bedstop with no micrometer, screw or other adjustment simply lock the saddle in position for the first groove and cut the groove. Hold the spacer up against the saddle and bring the bedstop up to trap the spacer against the saddle. Lock the bedstop stop down, pull out spacer, move saddle up against the stop and cut the second groove. Repeat until all grooves are done.

I'd prefer to go a bit beyond the simple bedstop by fitting a sliding rod and lock bolt. If there is no suitable machined surface on the saddle I'd also fit a suitable flat pad to the saddle to give a really good surface to register from. Choose the dimensions so you can add a micrometer later.

Need to generate the shape of single groove pulleys because the Vee is generally too large to be cut in one go with a simple form tool on home shop type machines. Basically you have to cut the two sides separately and maintain the correct spacing. So you are still stuck with getting the spacing right.

Clive

Thanks Clive, that all makes sense to me, I absolutely take the point about the small form tool. I'm actually in the process of making a bed clamp for a dial gauge which would serve the purpose for spacing.

William.

William,

It is a lot less faff making a poly V pulley than for a normal A series V belt. For these:

I set the topslide to be parallel to the lathe axis and just fed in for each groove with a 40 degree form tool. The topslide was moved by the appropriate amount for each groove using the topslide dial. The belt is J form, 6 ribs. I think 4 ribs would be adequate for your purpose. Another advantage, to me at any rate, is that I don't have to slacken off the tension to change the belt on the pulley but that may just be because I have a large distance between the centres. However, you don't need a lot of movement to disengage the belt.

Stay well,

Rod

William

Although I don't have one, I know that dial gauges mounted on bedstops are very useful for folk without a DRO.

Whilst you are at it do make provision to replace the dial gauge with a rod to give a positive stop for jobs like cutting up to a shoulder. I consider coming up to a hard stop much less stressful than watching a gauge.

Apart from the relative fragility the primary disadvantage of a dial gauge is the limited travel. Given suitable creativity it ought to be possible to come up with some means of temporarily fitting a vernier or digital "vernier" calliper to monitor the movement of the stop rod when pushing it up to the finish position with the saddle. The start point zero having been set by touching the tool to the end of the work before moving it clear to push the stop rod back. If it weren't for the calliper being upside down putting it on the tailstock side might be more convenient as there is more room at that end.

A fork shaped upstand for a depth micrometer (if you have one) might work well. Set the micrometer first then rest it in the fork. Move the saddle up until it contacts the probe. Lock saddle, lift out depth micrometer and set the rod to the saddle.

Or you could use an internal micrometer in a similar manner to set the rod for the longer cuts. Needs large enough setting surfaces to give something for the internal micrometer to work against but it seems feasible for all but the very smallest of lathes. I'd probably make the stop bigger to incorporate separate holes for the dial gauge and stop rod and a small flat face for the internal micrometer. Need more than one length of rod I expect.

I have a micrometer bedstop and six position rod type turret. The combination work well for me. But my lathe has an accurate travel indicator on the saddle.

Clive

19mm is the recommended minimum for poly-v in the usual pitch we use (which I can't remember off the top of my head - about 3mm?) That's what I used when converting my X2.

My conversion was featured in MW, some discussion of it here: www.model-engineer.co.uk/forums/postings.asp?th=81663

Neil

Hi

You may find this useful this method to fabricate Poly Vee pulleys. "J'Section = 2.34 mm.

Number of ribs + 2 6 X 2.34 = 14.04 mm. The outer flange can be a larger than the diameter by 2 mm to 4 mm than the tops of the finished Vees to provide a guide for the belt.

Eric

Ok, I'm convinced, poly v it is. Some further questions occur to me:

How many ribs? 4 seems common, but I have seen suggestions that 3 or even 2 would be adequate. Less ribs means less "stack" height which might be a good thing but more important seems to be the built in torque limiting safety factor - fewer ribs presumably slip sooner. The weak intermediate gear that we want rid of seems designed as a sacrificial component, primarily protecting the back gears buried behind the spindle which will be redundant anyway but is it realistic to hope that belt slip might reduce damage to cutters or workpiece perhaps in a misread decimal point sort of scenario? It might be interesting to make 4 rib pulleys and try running 4,3 & 2 rib belts to see whether slip could be provoked.

How necessary is the flange? Seems to me that it is only going to make speed change more awkward. If it is keeping the belt on when running then something must be seriously wrong with alignment.

Is there any reason to try to extend the speed range beyond the standard?

William.

Flange? I've never bothered with one, that's what the grooves are for!

I seem to remember using an online calcualtor that suggested 3 ribs would be OK, two would be 'optimistic'. Mine's a PJ belt, by the way.

Neil

I also scraped the base of the column bracket and added this, which makes big difference to rigidity.

Thanks Neil, is your conversion single speed? Looks like a 4:1 reduction which equates to the low range on the standard machine as far as I can judge.

William.

Edited By William Chitham on 25/06/2020 12:42:56