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Looking for a small quantity of Chrome Molly tubing . I dont work very well in Imperial, so have supplied dimensions in mm with my best guess in inches (Taken from variose charts):

 

About 1 m of OD 15.88 mm (5/8") x ID 0.534 mm 0.527") Wall 1.24mm ( 0.049")

About 500mm of OD 31.75 mm (1 1/4") x ID 28.7 mm (1.134")  Wall 1.47  mm (0.058")

 

I have taken my measurements in mm - checked out variose charts and "rounded" my  figures to the nearest/best guess listing.

 

Is it okay to purchase off automotive suppliers (rather than aviation) ?

 

Also

 

To fit inside  31.75 mm tube - I need to install (weld in place) a dividing wall, washer shaped piece of flat circular metal, with a 16 mm hole in the centre -  can this be purchased or do I make it ?

 

 

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Skippy, you need 4130 grade Chrome Moly steel, and this is the same steel grade that is used in both aviation and motorsport. Below is a description of Cr-Mo steel, from a Victorian supplier.

 

https://www.airportmetals.com.au/blog/chrome-moly-tubing-used-motorsport-aircraft-manufacturing/

 

You can buy small amounts such as you need, either online, from eBay, or from motorsport suppliers, who have online stores.

 

If you want the tubing quickly, I'd suggest Rod Andrews Race Cars, who are located in Seven Hills. They don't have an online store, you need to physically go to their business, and pick it up.

They state they have the sizes you require in stock, but I'd call first, to make sure.

 

With the current slow state of parcel and mail delivery, I'd suggest this is the quickest way to acquire the pieces of 4130 you want.

As to the circular piece of metal, Andrews may have an offcut of 4130 flat sheet, that you can make the washer-shaped piece out of.

You could use a stainless steel washer, but it will not have the same strength grade as the 4130, so I'd stick with some 4130 flat sheet.

Andrews will charge by the metre, and they will also have a cutting charge (per cut). It's likely they only sell in 1 metre lengths.

 

https://www.andrewsracecars.com.au/supplies.html

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Yep I've dealt with Andrews Race Cars, they're brilliant.  Had to order a piece only 200mm long once, they had no issues with sending it.

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Skippy,

Your best bet is to pop over to Bankstown airport and see Kyle at Aviation Welding.  9790 6481 He should have some off cuts that will suit you and it's all high quality aviation grade stuff.

 

image.png.0a19d5050b04a75dfad0e5b5b5d4054c.png You might have to make the doughnut yourself from some sheet.

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If you weld chrome moly and don' heat treat it afterwards, you are in a dark place. If it is annealed or stress relieved it's no where near it's optimum load carrying abilities afterwards either. If you don't stress relieve it you may/will have brittle spots where the weld has cooled too quickly and hardened at an edge of the weld. Some quite good frames can made in good quality low carbon steel tube. Nev

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You're foolish to weld high tensile and low-alloy steels without referring to the product manufacturers specifications and recommendations for post-weld treatment.

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I dont imagine I will be doing the welding. I describe my bush welding as sticking bits of metal together - no skill, no knowledge, no finesse. I was recently advised that when welding pipe/tube it is advisable to fill the tube with Argon - blew my mind!  I will purchase all the "stuff" and engage the services of a suitably qualified/experienced person.

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Just tell them it's for an aeroplane and see the reaction. It's your life.  I've seen a 30mm solid bar just clean break with  a small load when it was welded (very nicely)  into the end of a tube . Once you have above say .3% carbon you have strife. Read what is written on a Beech Bonanza or Debonair undercarriage leg. Nev

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3 hours ago, skippydiesel said:

engage the services of a suitably qualified/experienced person.

I recommend that you go talk to Kyle at Aviation Welding at Bankstown. He's probably the only person in Sydney who is approved by CASA to do aviation welding and who can be easily spoken to. Did you know that he has to pass regular competency examinations by CASA to retain his approval?

 

These are the hoops he has to jump through to retain his approval. 

 

33_1 (2).pdf

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Thanks again ALL - I have been in touch with Kyle of Aviation Welding - at this stage he is most likely to get this stunningly lucrative contract but I do have two, admittedly unlikely, leads to follow up on befor committing my hard earned $$$$

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I use Racetech. Use to use Performance Metals but after being sold a number of years ago have found them to be useless.

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On 21/10/2020 at 9:27 PM, old man emu said:

Kyle at Aviation Welding at Bankstown

You'll not only get the product you want, but Kyle has years of practical experience gained from undertaking a myriad of metal construction tasks. 

 

Just remember to throw the toy for his dog and scratch it behind the ear.

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On 20/10/2020 at 7:55 PM, facthunter said:

If you weld chrome moly and don' heat treat it afterwards, you are in a dark place. If it is annealed or stress relieved it's no where near it's optimum load carrying abilities afterwards either. If you don't stress relieve it you may/will have brittle spots where the weld has cooled too quickly and hardened at an edge of the weld. Some quite good frames can made in good quality low carbon steel tube. Nev

Depends how it's welded, I've seen fuselages welded with TIG, not stress relived and had no problems. Oxy/Ace stress relives it as you go, with any process as long as you don't do full long welds in one hit. There's a few old wives tales about welding.

 

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What I've put up is not based on old wives tales. . Your last sentence is not helpful. TIG is a very concentrated heat and rapid cooling  (chilling) of the weld edges a well documented problem. Some good welding is done by generally older welders with OXY but there the heat is less concentrated and it anneals itself as you ga (as you say). Oxy torch welding is not widely practised is it's slow and requires special skills and there can be a lot of distortion due to how hot everything gets. In any case the strength is greatly reduced by any heating done that is above the original temper figure. The only way to restore it is heat treat the whole assembly which is clearly impractical for large frame build and repairs.  That's why a lower carbon specification may be a better choice. It still has to meet the strength requirements of the design but strength is only what the weakest part is and you don't want brittle sections either. Nev

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Yes there is some truth to what you say but it's not a critical as is made out.

Just as an aside I held a CASA approval for OXY and TIG with both 4130 and aluminum. Never used it much and with having to sit the complete test at considerable cost every couple of years gave it up.  

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A don't doubt your qualifications but making light of it is not a safe concept to put out there.. Heat treatment after welding is always necessary in aviation for load carrying items.  It has to be separately signed off on the job sheet. Nev

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If you read it carefully there are risks of degraded welds including brittleness. It is also an advert for the firm mainly making roll cages which have carefully scarfed joints of more length of weld than the tube circumference. This is wise as otherwise the weld will be the weakest point because of reduced tensile strength due to the weld temp.. The two figures for different steels are given in the article. Load carrying members should not have sections that are weaker than the main part or they will be more stressed and that section will fail at a fraction of the life the part would otherwise. You don't even scribe lines on the surface of aircraft parts or use a graphite pencil on steel for exhausts or to be welded. Nev

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Cant help but comment:

 

I ask a question about propeller suppliers & their products - responses on topic - like getting blood from a stone

 

I ask a question about a bit of tubing - responses120%  amazing and, in some, a tad "snarky".

 

We are a strange breed!

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Facts are easier to manage than opinion.. Props are often a thing of MAGIC and expectations often disappoint. There's not much effectiveness in writing long articles here. It's a very diverse group   and less shooting of the messenger might help..No one is getting paid for any of this. It's done for general benefit of ALL. Nev

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