Early Roll Cage Mounting Plates

[chris_seven]

The very early 911 had a Roll Cage with large centre line radius bends in the main hoop and we have just made a batch of these cages.

We have been missing the early Cast Steel Roll Cage Plates which have the following Part Numbers:

901.803.231.21 and 901.803.232.21 shown below:



As we have just bought a set of NOS Plates we have decided to manufacture a small batch of plates (10 pairs) and if anyone is interested please contact me.

The plates will be cast from a low carbon steel using a traditional green sand technique. The material will be weldable and tapped to allow a roll cage to be bolted directly to the plate.

We will also supply a CAD drawn template of the correct mounting foot with each set of plates.

[joegt3cup]

I would be interested

[Brad Davis]

Hi Chris,

I would like a set.

Thanks for making these!

Brad

[chris_seven]

Visited the pattern maker this morning. The patterns are complete and we sand cast a pair of 'white metal' samples to check the dimensions, which were good.

The patterns will be delivered to the foundry for casting in steel on Monday. I expect the castings to be finished next week. We will then stress relieve and they should be complete by the holiday.

We have also started our next small project- Cast Aluminium RSR Spring Plate Covers.

We have drawn the spring plate cover in Pro Engineer as a 3-D model and will machine a resin component and 5-axis centre, which will be used as a pattern.

We will then sand cast these covers using a Petrobond casting sand to give a good surface finish.

We will cast them from LM25 Aluminium Alloy and precipitation harden them prior to machining.

We will supply them complete with bushes made from a modern equivalent to Delrin.

Should be complete by mid January.

[911pcars]

"The plates will be cast from a low carbon steel using a traditional green sand technique. The material will be weldable and tapped to allow a roll cage to be bolted directly to the plate."

Question: Why are you fabricating this by pouring a casting instead of fabricating from plate steel? Is this for authenticity?

Inquiring mind,
Sherwood

[chris_seven]

Yes, just that simple, we have some interest in the cast plates and the only ones I could buy from Germany were 650 Euros the pair and only one pair were available.

The roll cages we made have the correct centreline bend radius and are made from the correct 40mm OD x 2mm wall Cold Drawn steel tube and we wanted to finish them off with the correct plates. Cast Iron obviously won't weld properly hence low carbon steel.

[Flieger]

We have also started our next small project- Cast Aluminium RSR Spring Plate Covers.

We have drawn the spring plate cover in Pro Engineer as a 3-D model and will machine a resin component and 5-axis centre, which will be used as a pattern.

We will then sand cast these covers using a Petrobond casting sand to give a good surface finish.

We will cast them from LM25 Aluminium Alloy and precipitation harden them prior to machining.

We will supply them complete with bushes made from a modern equivalent to Delrin.

Should be complete by mid January.

Very interested in these. Clint's prototype rear bushings are taking forever. Will these work with torsion bars?

I currently have Smart Racing Products' rear spring plate bushings. They are a black polymer, and quite rigid, though slippery. Are you familiar with these parts? If so, how will your bushing material compare as far as deflection under cornering loads and with regards to friction.

Thanks.

edit: I suppose a new thread would be in order.

[chris_seven]

Max,

Yes they will.

The cast aluminium housings should be stiffer than the standard steel pressings as they have a much larger section.

Smart Racings bushes seem to be a PU based material and as such will have a non-linear Modulus of Elasticity.

It is difficult to know the stiffness as PU materials can have a wide range of properties depending on the application BUT castable material of this type tend to have a maximum Young's Modulus of about 60 000psi - equivalent to 400MPa.

This material will also have relativley high levels of friction and if it is not kept well lubricated may cause wear to the 'pins' on the spring Plate.

We are using a modern material Ertalyte-TX which has slightly higher modulus than Delrin (as used by Porsche) and lower stiction due to the use of an internal lubricant.

The Modulus is 3450 MPa (500 000psi) and its tensile strength is 76 MPa. Bothe of these properties are about 10% better than Delrin which has been used successfully for years.

Ertalyte Tx is also very resistant to water absorption.

[peekaboo]

My eye notices a differance in in the two sets of plates from the photos shown in this thread. The first set of photos (are these the NOS ones your refering to chris_seven , or some of the first you made ?) seem thicker , besides having the perimeter edges chamfered.

The second set (stored in the old Porsche label box , and that is a correct part number). Seem to be thinner gauge metal plate. And the perimeter edges not chamfered.

Are there two versions ?

It gets a bit muddled to figure it out by part numbers , as the late number is for a set (911.803.020.00) .

And I find two differant referances attached to it online , one listing this number (the set / 911 No.) to

1965-69, another to 1970-73 . Both of these referances are not from Porsche records though . But outside vendors.

I do see a differnce in physical manufacture from the two pictured sets though.

When I look again, the pair provided by Sithot has an additional bend (or at least , more severe , differant bend / s). So obviously 2 versions. Sithot's are for later models , or just differant ?

[chris_seven]

I agree that the plates I have look thicker - they were purchased from a guy in the UK that claims that they are new old stock but having seen the set in the box I am not sure.

I have sent the guy who bought them for his car the photograph as he paid around $600 for them.


I think the real difference is only on the edges and we will change our pattern so they are a better match.

The angle and number of bends are the same its just that our photographs aren't clear due the the light grey finish.

I hope our finished parts will be a bit closer to Sithot's clearly genuine parts.