Author Topic: To the Machinists out there... (Read 10031 times)

DugB · « **on:** October 01, 2008, 09:44:54 am »

Hello all,

So I tried to make the ball bearing conversion axle for my K2 4000 a few days ago...but there must be some small degree of misalignment to my small lathe, because I kept turning slightly tapered shafts...also, with my setup it's difficult to know when to stop...I accidentally shaved the shaft slightly below 12mm, at which point there was not enough lip to prevent the bearings from sliding all the way to the center of the shaft.

Anyway, that's not my question. :-) So I'm always looking around for shocks that will work on the rear of my 856's...and let's be honest, there aren't many out there that end with a female-threaded shaft or bolt hole. I know I can get new Risse's that will work...but new shock = new price, and I'm hoping to leverage the poor resale value of the used air shocks going on eBay.

Have any of the machinists on this list considered making an eyelet adapter for the X56/X57 rear strut so an eyelet-to-eyelet shock can be used? My mind envisions something like a block (with a threaded hole for attaching it to the strut top), with arms on each side that reach up to a cylindrical piece (positioned horizontally). The cylindrical piece would be removable (attached through the "arms" with a bolt), onto which the bottom eyelet for the shock could be mounted.

Such a piece would enable us to use many of the 7.87" (or smaller...realizing that the shock length doesn't *have* to be exact) rear shocks available. Anyone have the facilities to fabricate something like this?

- Doug :-)

Colin · « **Reply #1 on:** October 01, 2008, 10:57:09 am »

Yep, I'm sure these have been made and I'm pretty sure there's some pictures on here of them!

But.......IMHO.........I don't think the "cylindrical" piece should be horizontal or else it will allow a pivot point to occur at the base of the shock...............not good................I think it should be vertically aligned to allow a little bit of lateral flex but no vertical.

Col.

DugB · « **Reply #2 on:** October 01, 2008, 11:23:15 am »

Hmmm...I was thinking of a U-shaped piece of billet mounted to the top of the strut, with the rod going between the two uprights...the rod would go through the bottom eyelet to provide the lower mounting point. Are you saying that this isn't a good idea? OH WAIT...duh...I forgot that would mean three hinged points along the entire length of the strut/shock...yeah, that would be a bad idea without an additional, supporting link to the frame.

Another idea: drill a hole into the bottom of the shock eyelet...something large enough to support the shock well with no flex along the strut/shock combination. Then, insert into the shock eyelet a short section of rod tapped for bolt that will go up through the strut top, through the hole in the shock eyelet and thread into the tapped section of rod. The icing on the cake would be a piece similar to the black plastic pieces on either side of the ODS's top mount - with a semi-cylindrical cut in it to match the bottom curve of the shock's bottom eyelet.

Thoughts?

- Doug

benton · « **Reply #3 on:** October 01, 2008, 02:56:01 pm »

If your lathe is making tapered cylinders it means that the tailstock is misaligned. There should be a way to adjust it back into place to get a perfect cylinder. If the workpiece comes out too small on the tailstock end it means that the tailstock is positioned too far out (toward the operator).

I don't know exactly how most shocks are put togeter, but the eyelet probably comes off somehow. If you remove the eyelet entirely the shaft is probably threaded on its OD or ID. Either way it is easy to make an aluminum adapter that is a cone on one end and threaded on the other.

Post some pictures of the particular shock you want to make an adapter for and a sketch of the part you want to make. I have a shop and can make the prototype.

willem · « **Reply #4 on:** October 04, 2008, 09:21:09 am »

Guys,

Over the years, lots of your forebears have had great results building these U-shaped adapters for the top of the strut. And yes, the bolt MUST go fore-n-aft and it MUST NOT go side-to-side. I've tried other tricks and failed.
If you can find any of pictures of the work done by FrankD3000 he was a great Canadian machinist on the forum. If you IM him, he might answer.

Go get 'em!

Will

u02sgb · « **Reply #5 on:** October 06, 2008, 10:18:44 am »

Hi,
I'm also interested in attaching a new shock to a Proflex. In my case it's an 857 (medium so probably ok for conversion). I've done a (tiny) bit of research:

http://idriders.com/proflex/smf/index.php?topic=3034.msg21801#msg21801

Shows adapting the rear strut with two plates so you can bolt a shock to it. There's no (or minimal) lateral support for the shock so personally I'd not be comfortable with this. I'm also not able to weld so a bolt on adaptor would be better for me.

There's also posts from jazclrint who seems to have fitted a Fox shock on the back but I don't think he's ever posted any pictures.

I'm having problems finding older conversions as the links to the pictures have gone but the Frank3000 link I found was him talking about fitting a front shock which doesn't have the same problems.

Anyway, my idea would be to create an aluminium 'cup' for the end of the shock to go into, then screw a rod through the shock eyelet. The other side of the aluminium piece would be a cone that would screw into the strut.

Things that've occured to me:
1) It's pretty simple so why has no one else done it? (I'd have thought a small aluminium adaptor like this would sell as well as the replacement shock springs you see on here).
2) Would probably help to rotate one of the eyelets on the shock so the were at 90 degrees to each other. Not sure if this is possible, I'd been thinking about using a Fox float R or similar.
3) The length of the adaptor could be modified to cope with different shock lengths.
4) Presumably an air can will save a fair chunk of weight over the spring shock on it now?
5) Not sure where to find accurate dimensions of air cans to see if they'll fit in the gap in the frame.

Anyone else got ideas? All of the stuff I've searched on seems pretty old/incomplete/broken links.

Cheers,
Stuart.

DugB · « **Reply #6 on:** October 06, 2008, 10:53:54 am »

Ah, that's great! Nice to see the pics! The adaptor I was considering making wouldn't involve welding the strut, but would involve more precise machining of the adaptor (to match the face of the shock's lower eyelet) as well as drilling a hole in the end of the shock (through to the eyelet, but not out the other side). I'll try to draw some pics of what I'm talking about, but in general I like the designs in the linked thread much better! :-)

- Doug

u02sgb · « **Reply #7 on:** October 07, 2008, 02:24:24 am »

Also found some links from somewhere in Spanish (my Spanish is rubbish):

http://www.forumbtt.net/index.php?action=printpage;topic=11574.0

Which linked to this:
http://img172.imageshack.us/img172/4719/proflex1legendatg6.jpg

Keep getting the link to Frankd3000's gallery but it's not there any more.

Also found a link to Simon's Proflex, which he seems to have changed into a linkage system. Looks lovely but I think that would be somewhat further than I could manage. Frankd3000's previous posts are here:
http://idriders.com/proflex/smf/index.php?action=profile;u=441;sa=showPosts

One of the threads was saying that it's probably best to have the cone that fits into the strut for strength.

Stu.

willem · « **Reply #8 on:** October 07, 2008, 04:38:50 pm »

Stu,

You wrote "There's no (or minimal) lateral support for the shock so personally I'd not be comfortable with this. "

This is a regrettable shortcoming of the strut design. Whether you weld the shock to the strut or have complete lateral flexibility, your shock will not prevent side flexing of the rear swingarm.

If you get the vertical flex under control, you'll be fine.

DugB · « **Reply #9 on:** October 08, 2008, 07:47:14 am »

Hmmm...the idea I had would still reduce the side to side flexing because the shock would be rigidle mounted on the bottom. The U-shaped piece I'm envisioning is one where the u-shaped indentation in the block matches the outer curvature of the shock's lower eyelet. Then the mounting bolt comes up from underneath, through the bottom of the shock eyelet (requires a hole to be drilled) and then into a rod segment matching the shock eyelet's inner diameter and with a hole drilled and tapped through it to accept the mounting bolt coming up from underneath. This would provide a rigid mounting point.

As for what shock I'm talking about...well, that's the tough part. There are so many air shocks on the market and in different sized I'm not really sure which would be best. What air shock would YOU choose?

Ideally it'd be one that...

- could be used on the front as well (or a similar one from the same manufacturer)
- with the proper or slightly longer length (when including the extra .5 inch or so for the mount)
- is plentiful enough so that resale values are reasonable (and therefore I'd be able to find one cheap on eBay ;-)
- with readily available parts

Thoughts? If you can recommend one and I can find it cheap I'll give this idea a shot.

- Doug

rapiddescent · « **Reply #10 on:** October 09, 2008, 06:11:42 am »

if someone invents something that works well - and can get me an example. I'll pay for the design and the work you've done so that I can get a few hundred made up and put them on sale.

Any of these frames:
+ World Cup Frame 955. 855
+ World Cup frame mk 2, 757, 856, 956, XP Serries, 96 beast
+ 97 Frame: 857, 957, 97 beast and 97 animal

cheers
callum

benton · « **Reply #11 on:** October 09, 2008, 02:32:58 pm »

One of the other threads has a picture of a bent strut and there is a question of whether the shock is ruined too. Given that, it seems like attaching the shock rigidly to the strut is a bad idea; it can't take the sideload, so it doesn't add any stiffness to the frame.

Making a pivot on top of the strut that lets the shock move in the left-right direction might be the way to go.

keith · « **Reply #12 on:** October 11, 2008, 04:12:18 am »

Just changed a broken seat post. the seat clamp off the broken post is a threaded lug and a bolt. Was thinking of shaping the lug to fit the eye of a shock I have,drilling the bottom of the shock eye and bolting through the seat stay into the lug.Would this work? All feedback welcome

keith · « **Reply #13 on:** October 11, 2008, 04:16:57 am »

DugB · « **Reply #14 on:** October 13, 2008, 08:25:30 am »

Quote from: keith on October 11, 2008, 04:12:18 am

Just changed a broken seat post. the seat clamp off the broken post is a threaded lug and a bolt. Was thinking of shaping the lug to fit the eye of a shock I have,drilling the bottom of the shock eye and bolting through the seat stay into the lug.Would this work? All feedback welcome

Hi Keith,

That was what I was getting at in the posts above...but I was proposing also creating a U-shaped block to better support the eyelet where it would mount to the strut top. The bolt would pass through the hole in the strut, through the u-shaped block, through the hole drilled in the end of the shock eyelet and screwed into the threaded hole in the cylindrical piece that fits through the shock eyelet (similar to what you were thinking). I wanted to do this to fit one of the widely available air shocks that frequently go for cheap on eBay...but I don't know enough about them to know which would be best for the Proflex. Any ideas?

- Doug

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Author Topic: To the Machinists out there... (Read 10031 times)