RF-25 Belt-sizes and Table Stop Info Please

I've just bought an old Rong-Fu RF-25 mill/drill which is in need of a bit of TLC.

It has what appears to be two new belts but they are too long to set the right tension on the pulleys without fouling the housing. Can anyone tell me the right sizes for these belts please so that I can fit the right ones?

The table stops are also missing completely and so there isn't one I can copy. Could someone kindly take a picture of one to set me on the right lines please, or if there are better designs point me to one I could copy please?

Very many thanks

Jon

Why not use link belts? Run smoother too.

If you look at the seventh picture here:

**LINK**

You'll see one of the table stops. The front of the table has a dovetail slot cut into it so you'll need to make a pair of "nuts" to match the slot. The other parts are just a suitable size cap screw and a counter bored "button". I made new stops for my mill and think the buttons are somewhere between 3/4" and 7/8".

My mill actually has a dovetail slot on the front of the table and a T slot on the side so I had to make two different types.

I bought one of these machines 30 years ago from Graham Eng in West Bromwich, so it's got their Alpine nameplate on it not the RP-25 model number. But I'm pretty sure it was their model RP25 all that time ago, and the bigger one (RP35?) was too expensive, so I'm fairly certain it's the same machine. The pictures look the same ...

Anyway the point of this is that the two belts on my machine (which are the originals) are marked:

From spindle to idler cone pulley is marked A38

From idler pulley to motor pulley is marked A30.

Hope this helps, I wouldn't use link belt whizzing around that close to my hair line for all the love in the world - unless of course you always put the belt guard back after resetting the belts!!!!!

I've just converted mine to a three phase motor and a VSD. Great improvement, much more controllable, only sorry I didn't do it years ago.

Best rgds

Simon

Hi All,

Thank you very much everyone.

I feel a bit stupid because I didn't realize that I had the sizes already - Dooh! The values A31 and A38 are given in the manual - but in case Simon's machine is more representative I also ordered an A30 one too.

The link belts look good but I'll try the cheap and cheerful continuous belts and if they are very noisy I'll consider upgrading to the link belts then.

I don't know if I'm looking in the wrong places but there seems to be an approximate 7-10x price hike for the link belts which seems a bit steep unless the benefits are worth having...

...but I'll certainly bear it in mind when my lathe belt needs replacing to save dismantling the headstock bearings.

Many thanks again

Jon

Don't know if you'd get one the right size but I've bought most of my belts from Halfords or another motor factors.

I don't know how much movement there is with the pulleys for speed changing, I know that my Rexon mill has it's pulleys in line with each other, and there is not enough room to comfortably change speeds with a link belt, it takes a lot of heaving, and leavering with a large screw driver on my machine, and I had to enlarge the hole where the motor spindle comes through.

Ian S C

Slightly OT:

I wonder if there is anyone who, like me, has one of the early machines without a dovetail or tee slot for table stops? I put up with this for years until it occurred to me that I could fasten some extruded tee slot section to the table. This worked so well that I did the same for the Y axis.

As always, I could post a photo or two if this would be of interest.

Clever idea.

I wouldn't be without the stops on my VMC. As an aside, the stops can be a bit tricky to adjust when they're under the vice so I bought a Bondhus long reach ball hex T driver which makes things much easier.

Hi Ian,

Well it was the inability to tighten the belts which made me think the current belts are too long but you are right that perhaps opening out the hole for the motor shaft would give enough adjustment. It might be that just fitting a shorter belt is just as good.

Amazon have belts for about £3 delivered so that's my starting point. At that price it's hardly worth leaving the chair, let alone finding a Halfords

Jon

Hi again, the other modification I did to mine fairly early in its life was to fit a screw jack to the belt tensioner. At its simplest it's just a bit of all-thread from a bracket screwed to the RHS of the head casting to a pivot welded on the side of the motor mounting plate. The motor and its mounting plate swivel on two bolts on the LHS of the head casting. Originally there was a silly sliding peg and grubscrew affair to push the motor mounting plate backwards and tighten the belt.

Quite apart from this needing at least three hands to do, one of the main advantages of a belt driven machine is to be able to set the belt tension so the drive is firm enough to turn the cutter, drill etc, but if it all goes horribly wrong the belt slips rather than breaking things. Especially useful for drilling big holes! My experience with the peg and grubscrew arrangement it was originally fitted with was it was impossible to tighten the belt enough to drive properly - it's got a 1 hp motor and if you're drilling inch and a quarter holes you need the belt tight enough to transmit the torque of the motor. Otherwise you just keep stalling the spindle and chipping the edge off the drill.

If you're interested I'll show some photo's - it's a bit crude and made by a blacksmith (and an agricultural one at that!) but you'll get the idea. If I can work out how to upload piccy's...

Best rgds

Simon

And the other comment I wanted to make is that on my machine there is plenty of movement of the motor on its mounting plate to tighten the belts successfully with the belts fitted I've shown, without carving out a bigger hole in the top guard. That might be why one of the belts is an A30, not an A31 but since these are the originals I've never bothered to experiment and see the limits of the belt length tolerance.

Simon

Thanks for the idea Simon.

I must admit I did wonder about the tensioning of the motor belt in a better way but I wondered whether the more critical belt would be that for the final drive using the middle wheel which will have the greatest torque when the lowest speeds are engaged?

I guess time and experience will tell.

Thanks again

Jon

Vic:

My stops have shortened ratchet handles; tool-free but the handles sometimes clash and require re-setting.

BTW, my X axis tee slot doubles as a mounting for a digital scale.

Assuming you let the arm carrying the middle idler pulley "float" i.e. rotate about the axis of the column, the tension in the two belts is nominally equal. So you just do up the belt tensioner to tighten both belts the same amount.

I use mine mostly as a drilling machine, because it has a no 3 morse taper up the spout. It's a perfectly serviceable milling machine, but I haven't used it as such since the day I bought a Tom Senior vertical mill.

By and large I use the mill/drill for drilling holes where you need the spindle running at less than 200 up to 800 rpm (drilling 10 mm dia up to say 25 mm or so). In these conditions the belt from the motor is used around a very small diameter pulley, whereas the others are around bigger sheaves. This means that the friction between the smallest pulley and the belt is what governs how much torque is actually transmitted to the belt drive. You need a fair bit of tension to get the belt to sit properly in the groove of the tiny pulley on the motor shaft.

I've found my vsd allows me to do this speed variation without swapping belt positions. By using a VSD compatible motor (now there's a long story!) I get enough torque to do what I want to do and the belt stays put in one set of grooves. Yippee!

At higher speeds the whole machine is over-designed anyway, so transmitting enough torque to drill say a 2 or 3 mm hole can pretty much be done without any significant tension in the belts at all.

I tried uploading some piccy's - haven't worked out how to do it yet. I bet there are some instructions here somewhere in the forums.

Simon

Here's a picture of the screw operated belt tensioner. The longer column clamp bolts and packers (stacked nuts) on the right of the head stock are simply so you can get a spanner onto the clamp bolts without amputating your knuckles.

Here is a close up of the table stop parts in situ

And this is what the individual parts look like off the mill

Simon,

Thank you for the pictures - very much appreciated.

Jon

Hi again Jon - not that I'm obsessive about this, but...

You might find that the bargain basement vee belts selling on price on Amazon don't conform round the little pulley -groove shape of the lower speed driver pulleys. I bet these pulley sheaves are less than the minimum bend radius of the normal bog standard construction vee belt, and you may need something a lot more pliable.

My local bearing shop has sold me vee belts for funny applications before, and while they certainly cost more than you have mentioned, they did the job and lasted a sensible time. Those poor abused vee belts on a ride on lawnmower deck have a hard time...

If you're not happy with the results with your el-cheapo belts (poor grip, poor service life or possibly both) it might be worth your while to chat up a local bearing/transmission specialist shop and get them interested. Of course if Amazon does it for you good luck!

Rgds

Simon