Fitting horn blocks

[Peter Simpson 1Participant @petersimpson1]

Prior to fitting horn block do you.

1. Drill the frames then drill though to drill the horns.

2. Clean up the horn casting, drill the horns then drill through the frames.

????

[Peter Simpson 1Participant @petersimpson1]

[OldironParticipant @oldiron]

. The best thing to do IMHO would be to drill the part you can mark out the most accurately.

Then transfer the hole layout to the other part. Its seems to be a 6 of one and 0.5 of a dozen job

regards

[Neil WyattModerator @neilwyatt]

If the horns are ribbed, drilling them first avoids having a hole line up with a rib.

Neil

[julian atkinsParticipant @julianatkins58923]

Hi Peter,

As the horncheek castings (whether of cast iron or gunmetal) will be softer than the steel frames, then I would drill the frames first, checking of course that where you drill will avoid any ribbing on the castings etc. Then spot through one hole at a time into the horncheek castings.

Add temporary bolts as you go de-burring the castings as you go if gunmetal (easy if for 1/8" rivets and use temporary 5BA bolts).

When you rivet up, add all the temporary bolts etc and do one rivet at a time.

Then I put the 2 frames outside facing outside if that makes sense, then mill the final working faces in the vertical mill.

Cheers,

Julian

[Peter Simpson 1Participant @petersimpson1]

Many thanks for your replies. Julian your point about the castings being softer than the frame steel is a very good point. After fitting the frames back to back to machine the horn faces I have seen two variations on how to complete this task.

1, Mount the frames vertical on the milling machine table and use a long series end mill to machine the sides and top in one go. This appears the most logical but is prone to lack of rigidity an chattering of the milling cutter.

2, Mount the frames horizontally on the milling machine table. Use a slightly shorter end mill to machine most of the horn faces. The top and corners to be filled out as the milling cutter cannot access these area's. This method is much more rigid with the only down side been the need to file the top of the horns.

What would be your views be on the two methods ?

[julian atkinsParticipant @julianatkins58923]

Hi Peter,

For the final machining I use a long series end mill reserved for such jobs.

The frames are set up as you describe in the vertical mill with the frames horizontal and clamped together and bolted together. The horncheeks have already been machined before riveting to the frames. Less than perhaps 10 thou is taken off with the long series end mill to final size for the axleboxes to slide. The hornstay faces on the horncheeks are done the same time.

Years ago I used the same proceedure using the vertical slide on the lathe but the whole frame assembly had to be carefully repositioned for each hornblock pair.

What you want to aim for is as near perfect parallel and matching faces to the hornblocks/cheeks for the axleboxes.

Cheers,

Julian

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