Machining Hornblocks

[ron]

Hi Everybody,
I'm looking for a bit of advice about machining hornblocks from the more experienced.
What I was proposing to do was machine the outside of the hornblock castings where necessary, rivet them to the frames, bolt or clamp the two frames together 'inside out' [if that makes sense] then machine the cut out for the axle bearing blocks a pair at a time, is this a reasonable method or is there a better way?
Ron

[Jo]

Hi Ron,

I normally clean them up, rivet them to the frames, install the stretchers and buffer beams. Then mill each of the cheeks across the frame, using the milling machine compound table for squareness and indexing.

The advantage being that you don't have to worry about possible misalignment due to the stretchers. but you do need a milling machine with sufficient X-Y movement.

Jo

[Smifffy]

..I'm far from experienced :-)

But with mine, I did pretty much as you are suggesting until I came to finishing the internal faces of the horn blocks. At this point I assembled the frames, with Horn Blocks fitted, together as they should be with the stretchers (not inside out) and then clamped the whole lot onto my Milling Machine table, squared it up and then finished the horn block faces with an long series end mill - that way ensuring that the faces were square.

However, I suspect all that will go out of the window next time I take the frames apart!

In doing so I also bolted a couple of pieces of bar across my milling maching table and cut paris of slots in each the thickness and width apart of the frames, thus ensuring I had a fixing that aligned my frames totally square on the table. I have yet to remove these (although they do get in the way a bit) for future use.

This does assume that your milling machine is big enough to hold the frames complete. Mine is, but I did have to "slide" the frames along, because the longitudinal travel of the bed is not long enough to machine the front and rear horns (Royal Scot).

Hope this helps?

Mark

[GWRdriver]

Ron,
I am of the "clamp them together inside out" school of thought also, but I make one small addition. Somewhere on the frames in an eventually hidden location I add reamed holes through both plates into which dowle pins can be fitted so that when any machining is done on the frames they can be assembled or indicated into exactly the same position as they were when the cheeks were machined.

I don't claim this to be a great wonderous problem solver, but it does eliminate the concern that during subsequent machining of the paired plates you've got them back dead-on in line. This does require however that extra care be taken to get the mounting faces of your cross members machined square, but then this should happen anyway.

[ron]

Thanks for the replies, I like the idea of milling them with the chassis built up again, if my milling machine is big enough, I'll do it that way. It's a Simplex chassis which is too long for the mill but I should still be able to do it by remounting it on the table with a bit of care.
Ron