A3 guide yoke

[kenrinc]

I'm in the process of laying the guide yokes out. I had read about some of the confusion regarding this particular part in the "mistakes" section and am assuming that dimensions are good. This one is complicated! Anyway, all I really want to know is where to silver solder the guide blocks.

I know where to locate the piece for the running board.

On page 100, fig 16-6, left side, it looks as if the drawing has been slightly cut off, as if someone laid a piece of paper over it during duplication. I see a "2-x/8 = 1/64" It seems to reference a CL but I don't know if that center is the cylinder center or the top block center. Either way both dimension don't realy help with location.
How far down from the top of the part are the blocks and how far over?

Ken-

[Patrik]

Hi Ken

I'm not building the A3, but I have the book . Looking at page 100, my page looks something like what you described. But look at fig 16-5 p.100, look at the dimension to the far right, it says 2 7/8. And my book says + x/64 allowance for machining.

So my guess would be that the brackets centerline should be 3/4" from right edge. And the brackets should be at an equal distance from point that is 2 7/8 of an inch from the top corner. Look at the left view drawing in fig 16-5 p.100.

I hope this helps.

Patrik

[kenrinc]

Thanks Patrik! That was helpful! I did happen to catch that dimension after starring at it for awhile. The 2-7/8 x 3/4 is obviously the piston center line. That I have figured out, but my problem was the "equal distance" dimension of the blocks from this center-line (vertically). Those dimensions are nowhere. I finally figured it out after going back to page 98.

The dimension can be computed by using the drawing shown in Fig 16-1 left (pg98), where it shows the distance between the guides (.788") plus half the height of each guide block (.125 x 2) which equals a total of 1.038 which when divided becomes .519. Jeesh. Fig 16-6 "assumes" the user has all that figured out. I'm just guessing.

It's sort of odd because up to this point Kozo is pretty clear in his other fabricating drawings.

Ken

[GregMiller]

Ken,

Attached is the drawing that I did to help me out. I have completed the Guide Yolks, but have not attached all parts so I can not yet confirm that the drawing is perfect.

Hope you find it useful.

Greg

Attachments:

[kenrinc]

Wow, thanks Greg. I just think it's sort of interesting that Kozo shows that fabrication drawing with no reference for any of that stuff. I guess having to compute everything is part of the deal. Anyway, I'm over it. :-)

Were the dimensions on your drawing rounded up? Just looking at some of them, like the center distance between the two guide blocks is 1.038 not 1.040.

Ken-

[GregMiller]

Ken,

I typically don't round, although displaying some fractions with only 3 DPs sometime makes a 3/16 = .1875 show as .188.

The dimension in question has a range of 1.038 to 1.040. I measured my guide yolks and they both measure about 1.039....depending on how I hold my tongue .

When I drew this part, I likely chose 1.040 over 1.039 since 1.040 could more easily be halved.

Greg

[kenrinc]

Thanks Greg. I figured that out later. The reality is that that dimension is whatever it is... the point is it has to match with the back head flats. Very helpful drawing.

Ken

[kenrinc]

By the way, how did you go about drilling the three attachment holes? I'd guess that you'd measure, clamp the guides to the tie plage and drill them together but I guess you could mark and drill one and then transfer punch them. Seems a bit "fiddly" though.

Ken

[GregMiller]

I know that I drilled and machined most all of the guide yolk as a pair and only separated them at the end. I remember drilling the three holes and counter sinking one set, then flipping over to countersink the other set. I typically use the drill bit for hole alignment, then replace with the countersink bit.

Greg

[kenrinc]

Ah, so you clamped the two together and milled them as one? I'm guessing you hadn't silver soldered the guides and the board support yet? Kozo shows assembly first then machining which sort of insinuates machining after silver soldering but everyone's got their process. I'm building in 1.5" scale so the parts are twice the size and of steel. The amount of heat needed to silver solder is unbelievable. I ended up mig welding the mounts for the cross tie. I may do the guide yokes too but I haven't figured out how I'll cleanup the welds. They make it really hard on end mills.

K-