## Tiger I gearbox+steering mistery

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The Axis WWII discussion group is hosted by Tom Cockle and is dedicated to Axis armour of the Second World War.

# Tiger I gearbox+steering mistery

Joined: November 5th, 2008, 8:18 pm
Hi All,

There was a post some weeks aghttp://www.network54.com/Forum/47207/thread/1315407032 about accuracy of after market Tiger I gearboxes, and their eventual lack of accuracy. I have just had the chance to take a quite comprehensive set of measurements and pics of the Tiger I gearbox available at WTS Koblenz museum. I have a long term project of building an accurate Tiger I interior, so a research on this undocumented piece of the puzzle was mandatory.

After putting all dimensions together and "assembling" it into the Tiger I hull, I come to a very strange conclusion regarding the vertical positioning into the hull. I would like to share this, trying to clarify the issue.
For some of the dimensions I use the excellent David Byrden website, books data, combined with some of my own measurements.

I have decided to make a 3d model of the thing, as this tool allows a better geometrical analisys. Attached some pics, my 3d model still unfinished, specially the steering part which is quite hard to measure. While some small details are still missing, I think all the basic important dimensions and shapes are already there.

By "assembling pieces" I have reached a total length of 1808 mm, while Spielberger's spec for this is 1812 mm. The total length is, I think, impossible to measure on the real thing, that´s why I had to reach it as the sum of many many things.

Well now on to "the issue".
Let´s start with the attached the explanatory sketch (not to scale, just the relevant informations). I hope all dimensions indicated, combined with the text below, are understandable.

POSITIONING ASSUMPTION: the gearbox input shaft is horizontal (as depicted in any book) and at the same height as the engine output shaft.
- 370 mm is the height of the engine output shaft, measured from floor plate (source D. Byrden).
- 181,5 mm is the height from the input to the output shafts in the gearbox. This is indicated in Spielberger's Tiger I book, and all my gearbox measurements show this value to be correct.
- So 370+181,5=551,5mm the gearbox output shaft must be 551,5mm over the floor plate.

Verification of the assumption:
- The combat compartment floor is located 530 mm over the hull floor (D. Byrden)
- The gearbox top cover is around 200 mm over the combat compartment floor (source my own measurement in Saumur). This dimension was very hard to take, so we can consider it can vary some few mm.
- With my gearbox measurements, the output shaft is about 183 mm below the gearbox top cover.
- So 530+200-183 = 547 very very very close to the expected 551,5 mm, so the assumption seems to be correct, considering the doubt with the 200 mm dimension.

Moving on to the frontal part, we find the HUGE problem.
- The sprocket height over the floor is 295mm (source D. Byrden)
- The shaft line of the brake dics and the final planery gear is about 240mm * sin(45deg) = 170mm vertical over the sprocket (source D. Byrden).
- So in total 295+170 = 465 the brake dics + final drive input line is 465mm high over the hull floor.

The gearbox output shaft (551,5mm) must be, if placed as asummed, in line with the brake discs-final reduction shaft, but it is definitely NOT: 551,5-465 = 86,5 mm difference !!!!!!!.
I consider the difference huge compared to any possible measurement mistake I could do. I do not think the difference comes from any such huge error, so the positioning assumption must be wrong.

Possible solutions I thought of:
1) Move the gearbox downwards, keeping it horizontal: I think this cannot be done, as the measured distance from gearbox top cover to combat compartment floor (200mm) is about right. Even not taking care for this, additionally the gearbox cannot be moved downwards more than about 30 mm, as its lowest parts at the rear would get into collision with the torsion bars. I indicated this detail in the sketch.

2) The gearbox should be inclined (my check gave about 4 degrees) downwards, keeping the vertical position at the rear. The Shermans for instance have this kind of arrrangement. The transmision with cardan shafts (as it actually was) makes this arrangement possible. But this would imply that there is no book / diagram I know of, depicting this feature properly!!!. Some pictures available and some others I did myself, tend to support this theory of the sloped gearbox.
More: the gearbox is joined to glacis lower plate by means of an small shaft or rod diameter 40mm at the lowest part of the steering unit (see sketch). When placing the gearbox as assumed, a separation of around 125 mm is obtained; however pics show that this joint is not farther away than about 50-60mm. When the gearbox is "rotated", this issue is "corrected". See the following 2 pics where it´s clear that 125mm are impossible, as the rod clamped to the glacis lower armor plate is 40mm in diameter.

3) There might be a way inbetween, combining 1) and 2), which would make the slope angle less conspicuous.

So I made a "discovery" or the biggest mistake ever in Tiger research history.

Anyone has a Tiger in the back garden and can measure the distance from the hull roof to the gearbox, at both front/rear ends of its top cover?
Do I miss any additional pieces?
Any mechanic expert knowns the meaning of "Greatest angle of intermediate shafts: front 1, bottom 2 degrees"? This spec is given in Spielberger's and wonder wheter it might be of impact (and help) here.

Kind regards
Nacho Roces

Last edited by Nacho Roces on August 17th, 2012, 12:32 pm, edited 1 time in total.

Joined: May 5th, 2005, 1:38 am
Nacho,
I do admire guys like yourself. Seriously! Other than that, I can't help you with your issue. I saw the Bovington Tiger driving around back in March this year, and it seemed to be doing just fine with gearbox and all.

Regards from Germany,

Stefan

Edit: You may want to check pages 42, 43, 44, 45, 55, 73, 79, 103, 104, 105, 106 of the "Tiger Tank Owners' Workshop Manual" written by David Fletcher, David Wiley et al., published by Haynes Publishing, ISBN 978 1 84425 931 1
Last edited by Stefan Krakow on August 17th, 2012, 9:49 pm, edited 1 time in total.

Joined: June 23rd, 2005, 12:08 am
Hi All,

There was a post some weeks aghttp://www.network54.com/Forum/47207/thread/1315407032 about accuracy of after market Tiger I gearboxes, and their eventual lack of accuracy. I have just had the chance to take a quite comprehensive set of measurements and pics of the Tiger I gearbox available at WTS Koblenz museum. I have a long term project of building an accurate Tiger I interior, so a research on this undocumented piece of the puzzle was mandatory.

After putting all dimensions together and "assembling" it into the Tiger I hull, I come to a very strange conclusion regarding the vertical positioning into the hull. I would like to share this, trying to clarify the issue.
For some of the dimensions I use the excellent David Byrden website, books data, combined with some of my own measurements.

I have decided to make a 3d model of the thing, as this tool allows a better geometrical analisys. Attached some pics, my 3d model still unfinished, specially the steering part which is quite hard to measure. While some small details are still missing, I think all the basic important dimensions and shapes are already there.

By "assembling pieces" I have reached a total length of 1808 mm, while Spielberger's spec for this is 1812 mm. The total length is, I think, impossible to measure on the real thing, that´s why I had to reach it as the sum of many many things.

Well now on to "the issue".
Let´s start with the attached the explanatory sketch (not to scale, just the relevant informations). I hope all dimensions indicated, combined with the text below, are understandable.

POSITIONING ASSUMPTION: the gearbox input shaft is horizontal (as depicted in any book) and at the same height as the engine output shaft.
- 370 mm is the height of the engine output shaft, measured from floor plate (source D. Byrden).
- 181,5 mm is the height from the input to the output shafts in the gearbox. This is indicated in Spielberger's Tiger I book, and all my gearbox measurements show this value to be correct.
- So 370+181,5=551,5mm the gearbox output shaft must be 551,5mm over the floor plate.

Verification of the assumption:
- The combat compartment floor is located 530 mm over the hull floor (D. Byrden)
- The gearbox top cover is around 200 mm over the combat compartment floor (source my own measurement in Saumur). This dimension was very hard to take, so we can consider it can vary some few mm.
- With my gearbox measurements, the output shaft is about 183 mm below the gearbox top cover.
- So 530+200-183 = 547 very very very close to the expected 551,5 mm, so the assumption seems to be correct, considering the doubt with the 200 mm dimension.

Moving on to the frontal part, we find the HUGE problem.
- The sprocket height over the floor is 295mm (source D. Byrden)
- The shaft line of the brake dics and the final planery gear is about 240mm * sin(45deg) = 170mm vertical over the sprocket (source D. Byrden).
- So in total 295+170 = 465 the brake dics + final drive input line is 465mm high over the hull floor.

The gearbox output shaft (551,5mm) must be, if placed as asummed, in line with the brake discs-final reduction shaft, but it is definitely NOT: 551,5-465 = 86,5 mm difference !!!!!!!.
I consider the difference huge compared to any possible measurement mistake I could do. I do not think the difference comes from any such huge error, so the positioning assumption must be wrong.

Possible solutions I thought of:
1) Move the gearbox downwards, keeping it horizontal: I think this cannot be done, as the measured distance from gearbox top cover to combat compartment floor (200mm) is about right. Even not taking care for this, additionally the gearbox cannot be moved downwards more than about 30 mm, as its lowest parts at the rear would get into collision with the torsion bars. I indicated this detail in the sketch.

2) The gearbox should be inclined (my check gave about 4 degrees) downwards, keeping the vertical position at the rear. The Shermans for instance have this kind of arrrangement. The transmision with cardan shafts (as it actually was) makes this arrangement possible. But this would imply that there is no book / diagram I know of, depicting this feature properly!!!. Some pictures available and some others I did myself, tend to support this theory of the sloped gearbox.
More: the gearbox is joined to glacis lower plate by means of an small shaft or rod diameter 40mm at the lowest part of the steering unit (see sketch). When placing the gearbox as assumed, a separation of around 125 mm is obtained; however pics show that this joint is not farther away than about 50-60mm. When the gearbox is "rotated", this issue is "corrected". See the following 2 pics where it´s clear that 125mm are impossible, as the rod clamped to the glacis lower armor plate is 40mm in diameter.

3) There might be a way inbetween, combining 1) and 2), which would make the slope angle less conspicuous.

So I made a "discovery" or the biggest mistake ever in Tiger research history.

Anyone has a Tiger in the back garden and can measure the distance from the hull roof to the gearbox, at both front/rear ends of its top cover?
Do I miss any additional pieces?
Any mechanic expert knowns the meaning of "Greatest angle of intermediate shafts: front 1, bottom 2 degrees"? This spec is given in Spielberger's and wonder wheter it might be of impact (and help) here.

Kind regards
Nacho Roces
No offense dude, but who cares!!! What possible result from all this could happen.....build the model and be happy it goes together..............

Joined: January 20th, 2012, 8:25 pm
Your right, does it really make all that much of a difference in a model? Not really, but I know from experience researching models that it becomes a search for the truth. The ability to figure out details through rigorous thought (no matter how seemingly insignificant) that possibly no one has discovered, is pretty rewarding.

We know what we know about 70 year old AFV's because of a solid accumulation of hundreds of "insignificant" details like this one.

Joined: January 31st, 2009, 1:06 am
I can't help with the answers for the Tiger I tranny, but I can appreciate the search for the answers. I've been "down this rabbit hole" myself on many occasions and have always found the journey satisfying and finding the answers very rewarding.

There's no need here to criticise the desire for new (or newly re-discovered) knowledge, even if it's for its own sake.

Mike

Joined: July 18th, 2005, 2:10 pm
Your right, does it really make all that much of a difference in a model? Not really, but I know from experience researching models that it becomes a search for the truth. The ability to figure out details through rigorous thought (no matter how seemingly insignificant) that possibly no one has discovered, is pretty rewarding.

We know what we know about 70 year old AFV's because of a solid accumulation of hundreds of "insignificant" details like this one.
Inch by inch we come to greater knowledge. I think it's rather amazing that in many, many areas we know so much more now than what was available in publications much closer to the time of the actual events.

John

Joined: November 5th, 2008, 8:18 pm
Thanks to all of you for your encouraging words, I Knew it has a difficult question. Fortunately I also have had an offline contact who has provided some evidences pointing in the directions I suspected.

One other thing I perhaps did not state clear enough: the reason why to undertake such research. You don´t need to read the following if you are not specially taking care of dimensional accuracy.

The Tiger I interior is a very cramped place (I promise you) and everything is very very packed inside. This implies that when building an interior, a dimensional error, wherever it comes from, means that you have some few nightmares.
For instance, all the following parts/areas are dimensionally "connected" as if they were pieces of a puzzle:
- Torsion bars locations
- Engine firewall
- Hull roof supports, mid and front
- Ammo storage lockers, both on sponsons an on both sides of fighting compartment.
- Floor of combat compartment
- Transmision shafts.
- Gearbox and steering unit
- Brake discs, and final drive input shaft
- Add if you want the glacis armor plates, as they are so close to the steering unit.

Whatever you change, probably you are forced to change some or even many of them, so that you are able to fit everything in.

The BIG problem with the gearbox is that I have kits of Verlinden (3 versions) Afv-club, CMK and Royal model, and I didn´t know which one was dimensionally accurate. There sere several mm difference!! Which one should be used?. Not that easy, they are linked simultaneously to the rest of the tank by three points:
- Brake discs shaft
- Joint to the glacis at its bottom front.
- Rear gearbox support

In this kind of cases my approach is to start from the basics, this implies finding the right dimensions, positions, and then decided the best solution depending on the availabe kits' accuracies and how they can be fit at best in the puzzle.
In this particular case the solution is probably enough with the kit with total length closest to the correct value. But well, I like and enjoy to understand the situation "globally".

Cheers to all
Nacho Roces