Too Much Vacuum?

[concretecowboy71]

In my recent quest to track down all the weird noises that come from the lathe, I heard another strange noise when listening back to test cuts with no audio in them. I worked for hours trying to figure it out and finally decided run a cut and shut the vacuum pump down and see if the noise changed.

Sure enough, you could hear the pump shut down.

I have installed a Variac and am now running my pump at 1/2 the speed I did before.

It seems the lathe run 60volts AC to the pump and the variac I have will only take the voltage down to about 32 volts.

Has anybody else done any experimenting with pump speed or noticed this kind of noise before?

[mossboss]

Well known issue and quite common About 1/3 way up from zero for 50 HZ seems to be fine therefore or an educated guess would be about 1/4 up it should be about right for 60 HZ at 32 V you are about there a little lower may be better
This is a case of suck it and see/hear mate
Cheers

[concretecowboy71]

Thanks Moss man. I am going to get another variac that will allow me to get down lower. The one that was loaned to me will only get down to 32-volts, but has helped a lot.

[opcode66]

You also want to be sure that the small chip tube that is fixed to the SX74 cutterhead is not touching the black disc that it runs next to. If it is touching you will pickup noise in your cuts. If you put headphones on and jack the volume you will hear a faint whining noise in unmodulated grooves. I repositioned my small chip tube so that it was not touching the black disc and was as close to the stylus as I could get it but would also not touch the lacquer when the head is engaged. That worked a treat for me. I also installed a variac for control of the motor speed. Finally, I installed soundproofing material inside the lathe and encased the motor in it as well. Net effect was completely silent unmodulated grooves when played back at severe amplification. I came to the conclusion that it was the chip tube because the noise was mostly present in only one channel. Coincidentally the same channel the tube was next to...

[mossboss]

Ok Guys
Now if you look at the bend tube and it is Std Neumann it should flattened out in an oval shape as you looking at it face on where the chip goes in
The opening should be parallel with the straight bit of length of the tube when you look at it straight along the cut Over the years it may have been replaced with a bad alternative
If it is not like above than there are issues
Assuming it is than you need to have the back of the entry almost lined up with the stylus and parallel with the platter Make sure that it does not touch the larger tube sitting behind it with full movement of the suspension box
Adjust the bigger tube on its mount to achieve that
It does not get quite in the center it is always a bit of center
The chip should be entering the tube initially in the center than it gets sucked over to the side This also leaves a bit of a residue in the tube itself so periodic cleaning with Acetone is required, when over to over to one side it rubs on the tube
Remember that the velocity of a moving air stream is always higher closer to the walls of the ducting there is almost 60% less velocity in the center
Painful knees to get it right first time but not bad after that, once you know where it should be on your setup it takes a little more than 5 minutes
Compliments of Bernoulli and Reynolds
Cheers

[philbrown]

MEK works better for cleaning wayward chip.
It's pretty easy to set vacuum. Just make a test cut, listen to it and adjust accordingly. That is what I did, worked fine on both Westrex and Neumann.
Phil Brown

[mossboss]

MEK as in Methyl Ethyl Ketone has been banned in most countries Is it still obtainable in the USA?
It is a carcinogen not that cleaning of the little tube would give you cancer
And yes it is good I am a little surprised that it is still obtainable
Cheers

[opcode66]

Yes, you can buy it at Home Depot.

http://www.homedepot.com/h_d1/N-5yc1v/R-100210976/h_d2/ProductDisplay?storeId=10051&keyword=methyl&jspStoreDir=hdus&Nu=P_PARENT_ID&selectedCatgry=SEARCH+ALL&navFlow=3&catalogId=10053&langId=-1&ddkey=Search

I use acetone and a pipe cleaner.