Myford S7 Rattle - RC Groups
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May 16, 2005, 11:11 AM

Myford S7 Rattle

Hi all resurfaced again after a couple of days being poorly. Many
thanks to all those who offered advice and help re my possible change
to 3 phase VSD, I will be taking up the kind offers of help when I have
sorted my current problem and decided what to do next. Before spending
some money on a VSD for the Super 7, I thought I would ask some advice
to make sure that it is worth the investment.

Some time ago it developed a rattle when "free running" at the two
lower speeds of the high range (two pulleys nearest the rear of the
headstock) at the time I thought the motor drive belt was shot and
changed it temporarily for a link belt - noise disappeared. Having
bought a new belt I replaced it with the standard belt and the noise
returned. Yes I know I could go back to the link belt but I don't like
"covering up" problems.

As far as I can tell it is coming from the backgear key/bronze gear
attached to the spindle pulley assembly. I fiddled a 2 thou shim
between key and gear slot and the noise stops. What I can't work out
is why it is doing it with the standard belt and not the link type. To
get movement in that area the spindle must be momentarily slowing and
speeding up to hammer on alternate sides of the backgear key slot.
I'm also intrigued by why it only happens on the two rear pulleys. If
it is single phase pulsing why does it not happen on all pulley speeds?
Could it be the rear spindle ball bearings which are obviously loaded
more by the drive belt on those two pulleys? The spindle feels OK to
rotate by hand but I can't think of another solution. Having thought
about it as I write this I wonder if a change to smoother 3 phase would
cure (mask?) this anyway? Still most machines do not make this noise so
there must be something wrong.

Obviously, if I need to replace the backgear/pulley assembly (for which
Myford will need at least one arm and leg) and the headstock bearings I
will need to delay my change to VSD (orders from indoors). Any help,
ideas or advice would be much appreciated I'm sure I can't be the
only one to have this problem. The lathe is a late 70's power cross
feed S7 although I don't think that makes a difference. The spindle
main bearing is fine. Thanks in advance for your help.

Best regards

Easily confused of Wales

May 17, 2005, 09:11 AM

Re: Myford S7 Rattle


Thanks, it's always a comfort to know it's not just me. I hadn't
thought of the belt manufacturing but as it now has two new belts you
could have hit the nail on the head. Perhaps it will ease a bit when it
has done more running. Another reason for why they might have changed
to Poly-vee in the latest models.

I guess that if you already have a VFD you don't change belts that
often anyway; do you leave it on any particular pulley? I suppose it
depends on the typical size/material you are working with. Have you
found the VFD to be a worthwhile addition? Everybody seems to recommend
the change and tell me it's easier to accomplish than I fear. I shall
just have to lever the wallet open again.

Best regards