Clue to Linhof gear stripping problem?

[Darin Boville]

Frank has mentioned a few times in the past his experience that many Linhof's have the gears stripped on the rise mechanism of V's and Masters--the one's with the rise lever. Bob from HP Marketing sort of doubts that it is a design flaw.

I have two Linhofs and both were stripped. Their prior owners seemed unaware of it. So it does seem to be a common problem. But why? The ratchet lever is supposed to be designed to "give" if placed under too much pressure to avoid stripping the gears.

So I got one of the Linhofs back from Martin and had a little adjustment issue--he suggested that I tighten the little screws on the bottom front of the front standard. These hold the gears more or less tightly together. More highly and it is hard to move the front standard. Worked perfectly.

Here is what occurred to me--if too loose I bet the rolling gear can push away from the linear gear (don't know the right terms for these) and partially strip off the teeth of the plastic gear. If at the right tightness it seems impossible for the gears to strip, unless something is really bent.

Sort of confusing--sorry I'm not being more clear--but if you have the camera in from of you it will make more sense.

So, bottom line, is your Linhof's front rise gear stripped? Are the screws I mentioned loose? Is this the cause of the problem?

Note that the "correct" tightness on my cameras is just when the screw stops spinning freely. Not tight at all. Any tighter and the front standard is hard to move.

--Darin

[Leigh]

Hi Darin,

I'm not familiar with the Linhof, but I am quite familiar with gearing, so these are general comments.

The "rolling gear" and "linear gear" are called the 'pinion' and the 'rack', commonly a "rack and pinion" combination.
BTW, 'pinion' is just the common name for the smaller gear of a pair, or for any gear used with a rack.

There is only one 'proper' engagement for a gear set (or rack and pinion). If too tight it will bind; too loose will strip.

To set an adjustable engagement, first tighten it to the point that there's noticeable drag, then back it off just a bit,
until it moves smoothly. That's the correct setting.

If you buy non-OEM replacement parts, be sure to get both the rack and the pinion. They must match to work right.

The critical parameters are the pressure angle (commonly 14 1/2° or 20°) and the pitch.
These MUST be the same for both the rack and the pinion (or for any gear pair) or they won't work.

The diameter of a gear is determined by the pitch and the number of teeth.

Also, the face width should be the same, although if different it won't prevent them from working.

You can buy replacement racks and pinions from Stock Drive Products at www.sdp-si.com
They have a bewildering selection. Select the pinion by shaft diameter, outside diameter, and face width.
Those options will likely determine the pitch, which should be as fine as possible. Then select the matching rack.


- Leigh

[Andrew]

well, the *plastic* racks may not be a fault but they are certainly a weak point in the Technika design...

I have my doubts that making the rack out of plastic was an ideal choice when you combine it with a lever mechanism that allows you to generate a lot of force if the components aren't running smoothly. Everything is absolutely fine up to the point that the moving components start to get dirty and stick or they get to their limit of travel and then the plastic component are at risk of getting stripped.

There seems to have been a recurrent problem of people forgeting which way the lever is set to wind so they'd try to crank the standard up when the lever was set to crank down and, of course, that means excessive force on the plastic gears at the bottom of their travel and they strip off.

When I got my Master Tech the racks were ok but the lever mechanism was jammed up and I was offered the option of just converting it to a simple winding knob like the older models. The tech I dealt with [who's indipendent of Linhof] explained the problem of plastic gears getting stripped off and said it was common. Upside of the knob conversion is that it's intuitive, the lower mechanical advantage stops you stripping the plastic gears as easily and there's fewer moving bits to muck up. Down side is that I now rely on friction to hold the standard up [same as the older models like the III and IV] and the new knob sticks out the side a little bit further than the lever did so I lose some lateral shift when the standard is level to the drop bed struts or is inside the body. Overall, I'm happy with the conversion having been done as a fix on the camera when it wasn't working properly but I wouldn't do it to a new camera that's working perfectly.


addit
I'm not sure whether the lever is designed to "give" under excess pressure and I don't have one on my camera anymore to check but the mechanism on my example was jammed up and it wouldn't switch between rise and fall and there was no give in the system that I can remember. If there is any mechanism to prevent excess pressure it must be prone to malfunction...
.

[Bob Salomon]

I wouldn't do it to an older one as well! Linhof does not have a gear stripping problem with the system that they have been using since at least 1980 when I became the Product Manager for Linhof.
There is a mechanism that removes the force when the standard reaches the bottom or the top of the rack.
Now if you have a much older model that employeed a different system then maybe it was possible to strip a gear with excessive force.
But we do have users who give their cameras very heavy use, Sexton and Barnbaum to name two. And I have never heard from these people that there is a problem. And they will tell us really quickly if they or their students have a problem!

[Andrew]

so my Master must be pre-1980, I'll have to check the date

Bob, just to be very clear... I'm not canning Linhof, I LIKE MY TECHNIKA !!!

[Leigh]

I expect the rack is nylon, not "plastic".

Nylon is commonly used in gearing applications where weight is a concern and stress is not excessive.

- Leigh

[Frank Petronio]

Even if it does strip, it still holds tight, you just "help" the standard rise or fall with a gentle finger pressure. It's not ideal but the nice thing about the Linhofs is that even if they're broken, they're still more solid than anything else ;-p