Startrite Tilt Arbor - few niggles - any suggestions?

[CroppyBoy1798]

Hi guys,

I picked up a pretty decent c.late 70's early 80's Startrite Tilt Arbor 12" table saw, a few years back it was converted to single phase and has a 2.2KW (2HP) Brook Crompton motor fitted.

Saw is running fine after having the starter fixed however I'm noticing intermittent vibrations when the saw is turned on and the bracket that the motor is attached to seems to vibrate somewhat (more than it really should I imagine), you can almost time the vibrating moments, its like 'smooth......vibrate......smooth......vibrate', almost a shudder perhaps. All the bolts are tightened on the motor and bracket are secure and nothing appears to be worn or have any play in it (pivoting points etc).

Now, I havent got the saw bolted to the floor, but I dont think thats the issue, the saw itself is solid and not rocking, the vibration is emminating from the motor/raise/angle mech area and is confined to this area (but obviously I can feel it through the table and see it on the blade/riving knife..

What I've noticed is that the belts to be used in the saw are 7mX800's, the belts in the saw are 10X800's, could this be the root of the problem??

Thanks for any info/help! :wink:

 

[Shrubby]

Isolating the various elements could help:
run with and without the blade - I've had thin kerf blades cause vibration
run without the belt to see if the motor's OK
If the motor was replaced - was the bracket fabricated to use a foot mount motor in place of the eccentric flange seen in lots of startrites. could be misaligned
I use a smaller TA 145 but they are all similar in design
Matt

 

[CroppyBoy1798]

Hi Shrubby,

Thanks for the help, I've used both a 10" (2.4mm kerf) and a 12" (2.8mm kerf) with the same effect as far as I could tell. I've just had the belts off and tried the motor, she's running good and steady without any significant vibration (only what you'd expect from a powerful motor).

The motor is foot mounted. I couldnt tell what would have been the original type of mounting as the exploded diagrams I seem didnt include any motor mounts, as if this was specific to the user? or type of motor used.

Had a closer look at the belts too and they seem to have some uneven wear (thread showing through on one end, not on the other etc) so I reckon its down to the belts, they're not seating properly in the pulley, sliding from side to side, riding up the pulley wall etc.

 

[Stoday]

you can almost time the vibrating moments, its like 'smooth......vibrate......smooth......vibrate', almost a shudder perhaps. All the bolts are tightened on the motor and bracket are secure and nothing appears to be worn or have any play in it (pivoting points etc).

Classic resonance effects. As the motor speed varies slightly, the resonance peaks and fades. The effect should disappear when the motor's under load and slows down.

What I've noticed is that the belts to be used in the saw are 7mX800's, the belts in the saw are 10X800's, could this be the root of the problem??

Yes, that's probably the problem. A different belt with a different weight would possess a different resonant frequency.

You've probably seen the video of the collapse of the Tachoma Narrows bridge owing to resonance. If not, Click here

 

[CroppyBoy1798]

Thanks for the additional info! Appreciate it. I'm definately going to have the belts changed!!

Had a closer look at the pulleys today and I found that the motor pulley was 7mm further out than the blade pulley! :roll: So, after some work, and shimming I got both pulleys lined up and on the same plane. Vibration was more or less the same, but what I have found is that I've blown three fuses since I did the re-alignment!! #-o What the hell is causing that?! I read that belts that havent been used in a while take on a 'set' (the machine I bought hadnt been used in two years approx and had been kept in a pretty basic, damn shed, through some very harsh winters) so I figured the belts had been accustomed to the pulley alignment and now starting the motor (2.2kw) requires a bit more kick, blowing the 13amp fuse?!

 

[misterfish]

Although the saw will run fine on a 13amp fuse, the current drawn on start up is very high and will stress the fuse and cause early failure. My Wadkin table saw has a similar sized motor and regularly blew fuses in the plug that was fitted to it when I got it. I now run it on a 16amp dedicated circuit with a type C mcb, with the more sensitive type B it tripped out nearly 50% of the time.

Misterfish

 

[slowburner]

Hey CroppyBoy,
I had me eye on that saw!
I'm sure you've checked already but just in case - your blade's not warped, is it?
Might talk to you some time back in the other place!