VR: Disappearing Groove at Outer Edge. Why?

[ObiKutnobi]

Hi,

Hope everyone is cutting well.

I have an issue that im struggling to find a definite reason for. Occasionally, but still far too often. some cuts/blanks there will be a particular section (always the outer edge) where the groove disappears for approx 10mm to 25mm. Sometimes the anomoly will be consistent on both sides e.g.The same point of the disc, other times it will only happen on one side. Has anyone encountered this? and has anyone solved this? Please see pics.

Thank you!

groove disappear 1.jpg

groove disappear 2.jpg

groove disappear 3.jpg

[ObiKutnobi]

Probably should have mentioned its cut using a T-560 vinyl recorder

[handcut]

It's either runout on the platter or slight warping of the blank. Also, check your dashpot isn't 'bottoming out' or if the piston is rubbing on the cylinder, creating unwanted additional friction.

[ObiKutnobi]

Thank you Handcut! really appreciate you taking time to respond.
Don't mean to be a pain, but could i ask what do you mean by:

- "runout on the platter" - Do you mean the part where the souri rubber mat ends, leaving the blank hanging in the air?

- "dashpot bottoming out" - The point at which it is restricting the head from lowering any further right? it bottoms out when the stylus is about the same height as the actual platter. which is approx 2mm below the underside of the blank. Is that ok? or does it need more "headroom"

- "Piston rubbing on the cylinder" - Apologies for my engineering fail, where is the piston? and by cylinder do you mean the bar that carries the head across the platter?

Thanks, Obi

t-560 3.jpg

t-560 2.jpg

t-560 1.jpg

[ObiKutnobi]

Okay, so i've been a bit of a knob and jumped the gun firing questions back at you Handcut before engaging my brain in a calm manner. Please ignore all my comeback questions, I was under pressure at the time and shot from the hip. Sitting back tonight and re-reading it all makes sense what you said and i'd even add to the list the possibility of the suction tube touching the counter weight. Will get back on this tomorrow with a fresh head

[David34]

I had this problem when cutting picture discs.

My solution was to put the rubber matt under the disc (against Souri advice)

Problem solved. Hope this helps you too.

ps: im using Souri platter and motor too.

[Tellsan]

Are you cutting lacquer discs or some sort of acrylic?

If lacquer discs you might want to read the very last sentence on the attached word doc

Perfect Master Apollo.docx

if it happens with acrylic & your cutter is adjusted properly then chances are the discs are warped
If not then your cutting depth is being varied by some mechanical obstruction.

I once had that problem & it was the vacuum pipe/hose that was causing my problem. I had to relocate the path to make to make it work.

[tragwag]

double check that your head isn't touching the torque tube due to slight warp of the disc!
that's been the culprit in my case a few times