Gypsy 1/4” scale crankshaft material

[DaggersParticipant @daggers]

Hi All,

Am new to this group, I have a question regarding crankshaft material.

Looking at the Gypsy crank and trying to decide on the best material and balance the machinability against the strength.

Can you experienced guys out give me your best guess as I have no experience in a crank of this size/use.

[DaggersParticipant @daggers]

[JasonBModerator @jasonb]

EN8 on the drawings I have.

[mike TParticipant @miket56243]

I would go along with the choice of EN8 for the Gypsey crankshaft. It is a good compromise between strength and machinability. It is also readily available.

[DaggersParticipant @daggers]

En8 on order.

Am away from home at the moment so dont have the original drawings with me, did not realise steel spec was shown.

I have redrawn the crank on my laptop, which I have with me, as i found a drawing problem and needed to investigate before commiting to machining.

Does en8 need any stress reliving after rough machining and prior to finishing.

[JasonBModerator @jasonb]

Bright (cold rolled) will have more of a tendency to move than black (hot rolled) . What did you order and did you go for round or flat stock?

Edited By JasonB on 30/10/2018 07:40:15

[Ian S CParticipant @iansc]

Bright (Cold rolled) Will have a tendency to move, get hot rolled, the black stuff.

Ian S C

[DaggersParticipant @daggers]

Ordered round 21/4” diameter EN8M which i was told is the free machinng type of EN8. Not seen it yet but i presume it is bright bar.

[JasonBModerator @jasonb]

That's a lot of extra swarf when it would have come out of 50mm stock

When machining it flat I would take say 3mm off one side then flip it over and do 3mm off the other then back to the first for another 3mm and so on until you get down to thickness.

Then rough it out as shown on the drawing but a bit more than the 1.806 and leave for a couple of weeks. Then put in your ctr holes and machine.

[DaggersParticipant @daggers]

I agree, lots of extra swarf, but material came from a contact at cost who only had 21/4” round stock.

Would like to have purchased square/rectangular stock but i found it difficult to find supplier who would supply/ship small quanity at a reasonable price.

My first time working on an ic engine, had the plans/castings for years but other projects have got in the way.

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