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Hick Crank Overhead engine

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Jo:

--- Quote from: AVTUR on August 11, 2019, 05:51:37 PM ---I did not post the picture for fear of copyright.

--- End quote ---

Yes the image would be covered by copyright law. But copyright allows the sharing of a reasonable amount of a design for the purposes of discussion and I am sure Kirk will be more than happy if your documentation of your build results in additional sales of his castings, which I have provided a link to  ;)

Jo

Jasonb:
1.2mm milling cutters can be had fairly easily, MSC have several to choose from, I'm sure the extra 0.01mm over 3/64" won't be a problem.

As Jo says M2 fixings with old style hex proportions would be easier to source as well as taps & dies

AVTUR:
First: Many thanks to Jo and Jasonb concerning the picture of the model, 9BA threads and 3/64” cutters. I want to keep BA and ME threads since I do not like mixing different thread forms (or many forms on a project), seen too many bodged motorcycles. I am actively looking at the small cutters and have asked questions elsewhere on the forum. There may be more questions.

The fettling of castings has started. I got one fettled casting, the cylinder, shot blasted at “work”. I am just about happy with the result but filing marks will have to be finer (photographs attached). I do not have an air supply in my workshop so I have to rely on favours. The bedplate, its quality concerned me, is cleaning up very nicely. However I fear my Dremell may be reaching the end of its life. It was bought impulsively about 10 years ago and languished on the shelf for quite some time. About four years ago I found it made a good fettling tool and then, later, used it for parting-off very small items in a lathe.

During the fettling I found that the pump valve body casting (drawing attached) had a well-undersized dimension and that it was the mirror image of the drawing. The latter is of no consequence since it can be reversed without affecting anything. The undersized dimension has caused some thought:
1.   Do I try to squeeze the lost 0.05” into the remaining casting? I don’t really want to try.
2.   Do I machine a new one out of bronze bar? I don’t have any bar large enough although this is a sensible option.
3.   Do I build-up the casting by silver soldering a bronze pad onto the offending face? This is the likely option since I have small pieces of bronze and I like silver soldering.

This difficulty has uncovered a mirror drawing fault: the holes for the two studs that hold the valve body to the pump are also mirror imaged.

The drawing and understand of the components is continuing. More details and discoveries will be communicated later. I am itching to start machining.

AVTUR

Jasonb:
Depending on whether it is short at the bottom or top you could rearrange things so the error evens out a 0.025" top and bottom. As the part is not seen and I doubt you will be using it as a boiler feed pump that should not be an issue.

The soldering option would work too if you want to keep to the original sizes again depending on where the metal is missing either build up the top or bottom or if it is generally undersize all over then put a two bits top & bottom.

AVTUR:
It has been a week of minor disasters and difficulties.

The drawing of parts has progressed well enough for me to take a break and start making bits. I have not found any more errors other than one missing dimension.

Fettling is continuing and I have had a few more castings shot blasted [photographs attached]. The first “nasty” happened I tried to speed up the fettling of one of the two standards using the milling machine (I had to remove about 0.04” of material to get the correct outline of the casting). Holding the casting in the vice was difficult because of its shape. I convinced myself that it was held tightly and rigidly, even tried to dislodge it with a good tap from a small mallet. The cutter spat it out of the vice on the second cut resulting in some superficial cut/gouge marks on the casting. These will be filled with epoxy resin.

After shot blasting I skimmed the base of the bedplate [photograph of set-up attached] to get a flat base for the machining operations on the top surface. As feared, the aluminium was sticky and I had treated it as good aluminium bar. The finish was not good but no one will see it. Returning to it after three days I discovered two problems:

1.   The drawing distance across the bedplate for the model mounting holes could not be met. The drawing dimension is 3.250”, the maximum obtainable was 3.063” [see attached photograph]. So the holes were drilled 3.063” apart.

2.   The casting had bowed. On the long edges the mid-point was about 0.04” below the ends [see attached photograph]. Casting can stress relieve themselves and move when first machined but this magnitude was a surprise. Thinking about it the options were
a.   Make a second skimming cut – unwise, it might exacerbate the distortion since one is removing material from the stiffest part of the casting.
b.   Do nothing and see what happens (if the movement continues).
c.   Ignore the bowing since it can be lost by mounting the model only at the mounting holes. Skim the top pads carry which the cylinder and standards. Hopefully any resulting bowing will correct the shape. This will then require further skimming of the pads (the pads are thick enough to allow this). If there is no movement so much the better. Obviously the pads for the standards must be flat relative to each other so that the standards are parallel.
I decided on option c.

I skimmed of the pads (a largish diameter cutter, lower than normal speeds and white spirit gave an adequate finish), enlarged of the two major holes and drilled and tapped of small holes without any problems [see attached photographs]. I always use a guide for manual tapping, both for tapping and removing the tap. In this case the tapped holes are for studs so the small holes, 8 & 10 BA, were not through tapped. I could feel the tap tightening up as it approached the hard skin at the other end of each hole (discretion is the better part of valour, etc). Geoffrey King used trapped bolts to attach the standards to the bedplate. In this case I don’t why know he did this so I am using 4BA studs instead. The tapped holes are smaller than King’s square holes so I can revert to his design if necessary.

On inspection I found that the width of the large hole was well outside the nominal dimension. At work we had a 3Fs mantra – Fit, Form and Function. Function has not been compromised. Fit may improve the fitting of the cylinder. Form, very important on a model, may be slightly compromised at the base of the front, cylinder, standard. This can be hidden be a little bit of cosmetic machining [photograph of finished bedplate attached]. The studs, blacked, will be fitted later.

Now to clear up this morning’s silver solder session. There will be more next week.

I have to apologise for not including a scale in the photographs. Hopefully I will remember to do so from now on.

AVTUR

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