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Hi all. We are looking into a center lock nut system for this year and had some issues regarding pitch selection.
I was wondering what are the most commonly used pitch sizes for FSAE center lock nuts (if there is such a thing as a common pitch size)
We are looking at a M52 x 2.0 or a M52 x 3.0 thread with 120Nm of tightening torque. Both the hub and the nut will be made out of 7075 aluminium and anodised.
Any comments or suggestions would be much appreciated. Thank you.
Hi all. We are looking into a center lock nut system for this year and had some issues regarding pitch selection.
I was wondering what are the most commonly used pitch sizes for FSAE center lock nuts (if there is such a thing as a common pitch size)
We are looking at a M52 x 2.0 or a M52 x 3.0 thread with 120Nm of tightening torque. Both the hub and the nut will be made out of 7075 aluminium and anodised.
Any comments or suggestions would be much appreciated. Thank you.
No such thing as common pitch. I believe I used 1 1/4-18 UNEF for mine (It's been a few years).
You can get away with anodized aluminum, but you'll have to make sure all your tolerances are spot on before hand or that anodize will grow/shrink your threads enough that it won't fit. You can measure the hub threads easy enough by 3-wire, but how are you going to measure the threads on the nut?
With that, and the fact that inevitably you're going to have new guys monkeying around on the car, I opted for steel.. frequently cleaned with brake cleaner and lubricated. Just an extra factor of safety against threads getting destroyed, things galling, or cross-threading.
With regard to tightening torque, do you need 120 N-m? How much preload is that giving you? IMO the best route is to make your center nut a giant castle nut, and at some moderate amount of torque drill a hole through the hub and put a clevis pin through the whole thing. Clamps the wheel on with just enough force, but the clevis pin through the whole nut and hub assembly safely keeps it from going anywhere.
Hi. Thanks for the quick and detailed reply. I did consider the fact that anodising will tighten the tolerances between the male and female threads. I have spoken to our machinist and he reckons he can give us an additional room of around 25 microns or so for anodising since the anodising service we enlisted gave rather good tolerances. But I will have to look into this in more detail.
An alternative we considered was to anodise the hub but not the nut so this will wear the nut before the hub which can be changed much more easily and at a lower cost.
As for preload at about 100Nm the calculated preload we will get is around 9600N thereabouts. The 120Nm I stated was thought to be an additional safety measure but we may just stick to 100Nm in the end. Retention device has been designed into the system. It'll most probably be a cotter pin put through a hole which will rest snugly against the outer face of the nut.
My concerns about the system was more about the life of the system since we remove and retorque the wheels and nuts quite a few times every week. I was wondering if anyone has had problems like stripping threads frequently on the hubs or the nuts or some other problem since replacing the hubs would be a costly affair not to mention the downtime associated with it.
I have only had experience with a steel hub / aluminum nut combination, so I cannot speak of the Al/Al design you are considering. Whatever route you choose, my advise is regular maintainece and inspection of the assembly. Regularly wire brush & clean both threads, as well as the interface surfaces of the wheel/nut. Then apply some sort of dry-film lubricant such as Dow Corning 321 to all contact surfaces.
The retention method you mentioned sounds good, and is common place among many different levels of racing from dirt to open wheel.
If you are looking for a "common" component, have you looked at purchasing a center nut? There are quite a few race cars that use this retention method, so finding an off the shelf part may be easier (and cheaper) than you think! Whatever route you do chose, make sure that you have a number of spares on hand. Al nuts are wearable components, and DO have a finite life.
Jason Stuffel
-WARDJet.com
-Zips Racing Alum 03-06
9600N is a lot of force. But maybe that's reasonable.
Think for my 1 1/4-18 threads I used about 50 ft-lb and the castle nut / clevis pin deal. Worked great.
And then yea, as JD said, about daily or every other day I'd give a quick spray to the threads with brake cleaner, wipe the junk off with a shop rag, and then spray on a little of this good stuff.
Smells yummy. Sprays on and dries.
Wow. Thanks guys. I tried to source for a ready made center lock nut but could only find some HRP items. My mates have tried emailing them to no avail. Also tried searching this forum and someone mentioned Bishop Racing around 4 years ago. Can't find this company online too. In the part of the world I reside in its quite difficult to get our hands on racing parts since the motorsports industry here is almost non-existent.
Will give this Al/Al combo a try and get back to you guys again after that.
This Starret M1 lube sure looks the business. I've always known they make great machining tools with good value. Now I know they make great lubes too. Will try to find a can for testing.
Cheers
We get our center nuts from hyperracing.com
They should be able to help you out if you have any questions.
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