VR: Heat Affecting Dashpot?

[PMST]

Ok back to square one, issue is back, happened after 12 cuts today again as it got to mid day in the heat, very weird! I checked the head weight this morning it was 13g, I just checked now and it is 10g.

The back counter weight is still at the mark I made so that hasn't moved, same with black knob for the dashpot.

Any ideas what else might be worth checking?

With more weight the issue will be sorted, but I need to work out why as the day goes on it's getting lighter and lighter without the weight adjustment parts moving.....

[SueDenim]

Chief suspect for me would be the dash pot spring's tension changing with both the heat and after several hours usage.
I wonder if we can find a replacement spring from somewhere as I think I have the same issue...

[Vinylfan]

I doubt that the spring is the reason: I have only modest mechanical knowledge, but according to my understandig the spring only reduces the weight of the cutter head from 45g to 15g. The spring is made of steel, it is only stretched within its elastic range and not overstretched. Also, the spring is made of steel. For the elasticity of this material it is not important if the temperature is 20 or 50 degrees.

[MEGAMIKE]

hmmmmmm

is the diamond in tight/firm ?ive seen mine move at the begin of a cut before and it has skipped then gone back to normal all in a few grooves..also keep in mind that the most highest of tension is at the start of every cut on a 12 only and in the 1 to 2 inch area at edge

biglove

[Discomo]

I'm with Megamike here. Disconnect all parts in the arm, clean it. Oil it...
This is a mechanical problem and is probably caused by dirt build up.
Try this first. The oil/spring seems not very likely to me.

My first suspect would be the moving Iron piece between head and bar. If there's dirt blocking smooth movement maybe it's affecting the weight read-out on your scale.
Giving a read out of 13g when dirt sticks and showing 10g when there's free movement.
Also the skipping in the beginning may point at a situation wherein the movement is freed again.

A loose stylus doesn't affect weight...

[Discomo]

hmmmmmm

is the diamond in tight/firm ?ive seen mine move at the begin of a cut before and it has skipped then gone back to normal all in a few grooves..also keep in mind that the most highest of tension is at the start of every cut on a 12 only and in the 1 to 2 inch area at edge

biglove

I've also had this problem once. (But I don't believe this is applicable here)

I find it a flaw in the design of the VR that you need to wriggle this stylus in with a certain amount of force. It causes some problems for me sometimes to get it in, especially when I can't use an appropriate tool.
It would be so much better when it had a bayonet click system of some kind. Simple, steady without the risk of damaging anything.

[markrob]

I'm not a VR owner, but I had some thoughts.

Have you checked to see if the dashpot is damping the head movement properly. If you float the head and give it a slight tap, does it oscillate a few times before settling down? That would indicate that its under damped and may need a higher viscosity oil. If its over damped, is it sluggish settling down? That would indicate the opposite issue. It would also be interesting to try the experiment dead cold and then after heating the dashpot and other areas with a hair dryer to see if the behavior changes.

Another thing to look at is if the undamped motion of the head (no dashpot oil present) is being hindered by bad suspension bearings or some other friction due to rubbing. Friction/ sticktion can act as a damper, but unless its controlled, the results could be variable especially with temperature.

Hope you find that helpful.

Mark

[PMST]

Massive thanks for all the suggestions, i will look into it all! Dashpot/spring sections has been stripped and cleaned, i will look into the bar through the block connecting to the head and other bits for dirt, ill give the lead screw a deep clean and will try the head oscillation idea with it suspended! Unfortunately i have some being done on my house so cant do this for a few days but will report back with whatever i find!

[PMST]

The issue has reared it's ugly head once again! Yesterday at 2pm, 33 degrees outside (much hotter inside) and i had been cutting all day, so the VR had a lot of use that day. I've been reading the points people made and testing things, so due to the metal, sounds like the spring can't change tension, the head seems suspended well in the new oil, the 10mm nuts on the side of the head block are tight, but what changed this time was the head weight hadn't changed.

Previously the head would get lighter towards the end of the day, but since cleaning the dashpot and changing the oil, this seems to have rectified that, but still, later in the day after many cuts and on a hot day, i'm getting skipping on the lead in grooves and nowhere else.

So, i think the next logical step, like a few people said here is to take it all apart, clean, lube and reassemble. I wanted to check here first does anyone have any pointers? Anything i should watch out for? Or is it generally straight forwards dissembling the head from the head block and lead screw?

[soeffingodly]

The issue has reared it's ugly head once again! Yesterday at 2pm, 33 degrees outside (much hotter inside) and i had been cutting all day, so the VR had a lot of use that day. I've been reading the points people made and testing things, so due to the metal, sounds like the spring can't change tension, the head seems suspended well in the new oil, the 10mm nuts on the side of the head block are tight, but what changed this time was the head weight hadn't changed.

Previously the head would get lighter towards the end of the day, but since cleaning the dashpot and changing the oil, this seems to have rectified that, but still, later in the day after many cuts and on a hot day, i'm getting skipping on the lead in grooves and nowhere else.

So, i think the next logical step, like a few people said here is to take it all apart, clean, lube and reassemble. I wanted to check here first does anyone have any pointers? Anything i should watch out for? Or is it generally straight forwards dissembling the head from the head block and lead screw?

Bummer.

I am also curious about this. Seems pretty straight forward but it would be nice to hear from someone more experienced with the unit.

Good luck man, hope the breakdown and reassembly helps to rectify your issue! I know I'd be going nuts.

[PMST]

Yeah its a pain, but if i start cutting early and finish before the mid day / afternoon heat i have no problems, which maybe is a good thing, get work sorted earlier! I think it's just a case of maintenance, the machine gets a lot of use and it's a mechanical issue, so will get it sorted soon as i find the time.

[PMST]

Update! A friend on here mentioned that I should try cutting at 33rpm, rather than 45rpm when the problem occurs, so I did this, and the problem is not there. This implies its down to a change in the viscosity of the dashpot oil when parts heat up not regulating the plunger properly, so now to try new oil for the hottest summer months....

[SueDenim]

Hi again,

Something just occurred to me as I was doing some routine maintenance of my own VR today which might be relevant to the variable groove depth problem we've both had.
It concerns the dash pot plunger and the threaded rod it's attached to... That threaded rod passes through a metal cube which is fixed to the main head suspension using a hex screw.

Is your metal cube screwed hard against the head suspension or is it slightly loose and free to move?

[PMST]

Thats a really good point, i've actually taken it apart and as i took the cube off it crossed my mind! I'm putting it back together and wondering this.... What's your thoughts on it? I've serviced the full machine, however i didn't have Souri's dashpot oil.... so i'm gonig to try some SAE 50 oil, or maybe 40, off advice from a friend

[PMST]

Before taking it apart the cube had movement, wouldn't say it was massively loose, but had some movement

[DJ2000]

some movment in the block is good, if its tight the rod that goes through it will catch and cause depth issues it was one of the things I went through checking when i had outter groove issues

[Discomo]

There is very slight movement of the block if you move it from front to back (because of the hole in the block) but not any movement from left to right. It's screwed tight to the overhead.

[PMST]

I wonder if over time that cube part had become stiff from dust and dirt, meaning the plunger wasn't acting correctly? As soon as i get some oil i can test it, going to try to sort some today

[Discomo]

The plunger doesn't do that much. It doesn't affect the depth of cutting.
Just look how it works... when you lower the head, the plunger moves down until the black winged screw touches the block. From there the spiral is taking over and that's the only section which affects the depth of your cut. Plus other moving parts- the only moving part which is the big block between head and overhead.
The plunger and winged screw and (little) block are only there to keep everything in position for the spiral to work correctly.

[SueDenim]

i'm gonig to try some SAE 50 oil, or maybe 40

That's a good point - maybe we can do a quick straw poll...
What weight of oil is everyone using in their VR dashpot?