Inconsistent groove depth - Presto 75A

[FFrankensteinRecords]

So I'm having this issue where my grooves will randomly disappear for a split second, like the cutterhead became lifted up briefly, creating a dashed line looking effect in the groove. It does this completely at random it seems, it's always in different places, just once or twice here and there. Sometimes I can cut 20 records with no problems, and then other times (like this very moment) I can cut 5 records in a row and it's all over the place, ruining the records. It seems that there are also less pronounced spots where the groove will go thinner then thicker over and over, like its being slightly lifted repeatedly. It creates a strange spiral looking effect on the record when the light hits it right. What could be causing this?? I'm embossing on poly with a 1-C, there's no contact between the disc and the cutterhead body, no warp on the blanks, nothing on the surface of the blanks, nothing like that. I'm utterly stumped. Has anyone else experienced this?

[Jccc]

maybe be it could be that the feedscrew is not lined up?

[emorritt]

The 75 doesn't use a feedscrew, it's a worm/gear assembly that uses a wedge-shaped gear to drive the arm across the disc. Sounds more like your head is mounted too high and is not clearing the lift/drop completely when in the 'down' position. There is also a spring that is used to set groove depth. This may be too tight and needs to be adjusted.

[Steve E.]

I think emorritt is probably dead-on.

Another thing I have found that can cause this effect is a bouncey old wooden floor. Subsonic rumblings, from walking on a trampolining floor, can make a groove disappear. I had all sorts of troubles along these lines in my old apartment.

[FFrankensteinRecords]

I've got a pretty good amount of weight on it and the head is mounted as low as possible so I don't think it's that.
After a little messing around I think the floor problem might be the ticket, I've been able to recreate the effects by lightly hopping around.
My house has hardwood, only lived here for about a year now.
Any ideas on ways to insulate the lathe against that sort of thing?
Thick rubber mat maybe?

[mossboss]

Find a flat piece of concrete and sit it on it, as heavy as possible, 100lb or more, it will fix it.
Best