Variable speed VMB

This topic has 11 replies, 6 voices, and was last updated 24 July 2016 at 11:55 by John Haine.

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22 July 2016 at 10:10 #247546
Douglas Johnston
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@douglasjohnston98463
I have owned a 3 phase inverter driven Myford VMB mill with poly-V drive belts for a number of years and have always had it on the same pulley setting. The great benefit of inverter variable speed drives has made this possible.

However I now need to change the belt positions to get a higher torque low speed setting and have hit a snag. The middle pulley has to be moved to change the belt positions but four bolts have to be loosened to do this. No problem you might think, but they are almost impossible to reach since they are tucked under the bottom poly-V pulley and none of my spanners can get anywhere near them.

The manual that came with the mill is no help since it only mentions the older V belt version where there is easy access to the fixing bolts.

Is there anyone out there with the same mill that has found a solution to this problem?

Doug
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22 July 2016 at 10:10 #32738
Douglas Johnston
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@douglasjohnston98463
22 July 2016 at 10:18 #247548
Michael Gilligan
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@michaelgilligan61133
At the risk of appearing frivolous, Doug [which is not my intention]

Presumably, all you need is a thinner spanner.

What size are the bolts, and what reach do you need ?

MichaelG.
22 July 2016 at 11:01 #247558
Ian S C
Participant
@iansc
An angle grinder is a good tool to start modifying a spanner, ie thinning it down to fit a narrow gap, or you might find some sets that are made of 1/8" pressed steel.

Ian S C
22 July 2016 at 11:08 #247559
Gordon W
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@gordonw
Spanners can easily be bent to suit odd jobs- gas blowlamp. Find a spanner that will fit the nuts, long enough to reach then bend and thin to suit. I've got odd shaped spanners that I can't remember what they are for.
22 July 2016 at 19:20 #247638
Douglas Johnston
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@douglasjohnston98463
You are quite right Michael, it's what I will end up doing, I was just in need of a good moan at the design engineer who thought that 4 inaccessible bolts were a good idea for something that needed adjusting. It is quite clear that when the drive system was redesigned for poly-V belts they just used the same base plate as before with total disregard for the inconvenience caused to the user. I expected better from Myford.

The bolts are 8mm metric (13mmA/F ) with all sorts of obstacles in the way so the spanner will have to be very thin and short, and with my luck the bolts will be really tight.

I feel much better now having had my rant.

Doug
22 July 2016 at 19:34 #247639
Michael Gilligan
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@michaelgilligan61133
Doug,

It's a Model Engineering site … So I'm sure no-one will object if you let off some steam

MichaelG.
23 July 2016 at 10:51 #247719
Ian S C
Participant
@iansc
If worst comes to worst you might have to move the pulley up the shaft a bit, maybe only a few mm, you might be able to move the other pulley to match, and leave them that way.

Ian S C
23 July 2016 at 20:07 #247791
Douglas Johnston
Participant
@douglasjohnston98463
Nice idea Ian, but it's a non starter with the way the pulleys are fixed. I solved the problem this afternoon by adapting a 2mm thick pressed steel spanner to give an overall length of about 8cm. It took ages to locate the spanner on the bolt heads and it is just as well I won't need to this very often in future. I still can't believe Myford could supply the machine with this design flaw.

Doug
23 July 2016 at 20:20 #247794
Michael Gilligan
Participant
@michaelgilligan61133
Now that you know what fits, Doug; it may be worth replicating your spanner in Gauge Plate.

I don't know what obstacles are in the way [maybe you could give us a few photos], but the ideal might be to make some sort of Crow's Foot, to be operated by a small ratchet.

MichaelG.
23 July 2016 at 20:24 #247797
Baz
Participant
@baz89810
Douglas, I purchased a Myford VMB varispeed brand new from Myford and it was supplied with various spanners, one of which is a Snail Brand 12 and 13 mm open ended bent at 32 degrees to access these bolts.
24 July 2016 at 11:55 #247859
John Haine
Participant
@johnhaine32865
When I converted my VMB to 3 phase I removed the central pulley, which is nearly the same as the spindle pulley, and fitted it to the motor instead. I reckoned there was no need for it with a vfd, and I haven't missed it at all. Also fitted a link belt rather than standard vee belt, altogether a big improvement in smoothness and versatility.
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