Belt problems with an Alpine DM25

I've had this mill drill for many years and don't often need to change the speed but when I do it's a real problem.

My other belt driven machines have it arranged that swapping from one set of pulleys to another is easy because the pulley diameters mean no change in belt length, but on this DM 25 the only way to do it is to change the belt length and so far I need 6 different lengths of belt.

Has anyone else come across this problem?

Brian

Summat might odd with this.

Before I make a fool of myself making all sorts of irrelevant suggestions, could you put up a photo or two of the belt drive aspect of this to show the parts involved?

Look forward to helping out.

Simon

Thanks Simon; I have taken 2 pictures with the same belts fitted. The first one shows that the belts are a good fit and drive properly.

The second picture show the same belts but on different pulleys. If the motor is swung back to apply tension then the pulley or the motor shaft catches on the casing making a dreadful noise and no tension can be applied.

Any help gratefully received.

Brian

Should be easy to adjust, very similar to my drill. Three pulley sets centre one on a pivoting arm and the tension applied by sliding the motor back and forth.

The image on the inside of the lid shows how the belts fit on the stepped pulleys.

The lever to the right of the start switch pushes the motor back and forth. Shouldn't need different lengths as the belts are always on paired stepped pulleys so minimal change in length. Unless your machine has been altered in some way?

Update: you posted the image whilst I was typing - that front pulley looks very odd on all the similar machines I have seen the stepped pulleys have equal steps making length variation minimal. Only solution I can offer is to get a matched pair for the centre and front pulleys.

John

Note: liberated this image of DM25 from lathes.co.uk

Edited By Journeyman on 01/06/2020 14:03:19

Edited By Journeyman on 01/06/2020 14:09:08

I have come across two pictures of an Alpine DM25 online - one appears to be the same arrangement as my RF30, with an idler pulley & two belts. The other looks like an oversized pillar drill with what appears to be a direct connection between motor & spindle via a single belt - as the OP states "6 different length belts" I guess his machine is this type.

On this type of arrangment it is usual to take up the tension by pivoting the motor mount - the RF30 works this way & the picture I found of a single belt DM25 shows a motor plate clamping handle on the star wheel side of the head casting near to the motor, suggesting that this method is used on the single belt machines as well. Slackening the clamp should allow the motor plate to move in an arc from a vertical pivot shaft on the return spring side of the casting.

Nigel B.

(further info posted while I was typing !)

Edited By mgnbuk on 01/06/2020 14:26:28

There's something not right here.

I haven't understood how the second (front) belt is tensioned - there seems to be some sort of screw under the edge of the intermediate pulley.

On my RF25 (Alpine Engineering badged) the intermediate pulley stack is an idler mounted on an arm swinging around the centre column. For all combinations of belt and pulley positions the movement of the motor is sufficient to tension the pulleys. It gets a bit close the the limits of the guard in some combinations, but it does work provided the belts are the intended length.

Swinging the motor tensions both belts. Is that the case with this machine?

I wonder if the second belt (on the spindle) is a bit too long - using up more than its fair share of free travel?

Ostensibly it looks as though the machine has been fitted with the wrong pulleys from birth - but that statement has other ramifications.

Would you like to measure the OD of each sheave on the three cones, and also if possible identify the length of the belts as fitted. Oh, and the nominal speed of the motor.

Then a photo of the label showing the nominal spindle speed for each belt position please.

I think I've got a programmable calculator program to calculate the PCD length of the belt path for a given shaft spacing and sheave size somewhere, if not there's sure to be one on the 'net. We can then model the dimensions of the drive and see what's going on.

An intriguing riddle, but it's only geometry.

Best rgds Simon

Thanks for the replies. As to the intermediate pulley stack, this is mounted on a plate that slides longitudinally between the other to pulleys and adjusts (or not) depending on the belt sizes.

The motor swings to apply tension but only to a limited extent before the shaft or pulley make contact with the casing.

Simon, I'll try and get you the answers although, short of changing to different pulleys, it's not easy to think of an answer, apart from carrying on as before and getting another couple of belts.

Brian

Edited By Brian H on 01/06/2020 14:56:50

Is there any way to increase the swing of the motor? Would changing the length of one or both belts help.

The drill mill at the museum manages all the changes ok, but the belts I bought to replace the originals did not work, I had to get some very similar lengths.

That middle pulley has a limited swing, are you sure it is not being brought up against its stops by the belts being the wrong length?

If you have the time you might get a length of link belting and then you can experiment. I would think the manufacturers would have done the sums regarding belt swapping when designing the mill.

Is there any way to increase the swing of the motor? Would changing the length of one or both belts help.

The drill mill at the museum manages all the changes ok, but the belts I bought to replace the originals did not work, I had to get some very similar lengths.

That middle pulley has a limited swing, are you sure it is not being brought up against its stops by the belts being the wrong length?

If you have the time you might get a length of link belting and then you can experiment. I would think the manufacturers would have done the sums regarding belt swapping when designing the mill.