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The dreaded drilling job!

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Tony Martyr20/02/2012 16:16:05
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I have spent many hours machining the cylinder blocks of my Bolton design TE engine (see album) and I am very pleased with the valve ports and the through drilling of the exhausts.

But I now have to drill the inlet holes from cylinder rebate into the base of the inlet ports. 5 x 6 chances to get the (different) angles wrong, break a drill in cast bronze etc.

I hate this job - my loco cylinders were OK but I am glad the holes aren't on show since they all break-through into the valve ports at slightly different heights.

I can't see any other way to do it rather than setting the cylinders at an angle in the machine vice 'by sight' and starting the holes with a very small slot drill or centre-drill - any tricks of the trade of which I am unaware?

Tony

tractionengine4220/02/2012 16:44:53
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Tony

I cannot remember the exact arrangement but there was a method given in ME similar to that shown below. This arrangement allows you to position the drill and determine the drill exit point.

Drilling cylinder ports

maybe others have used this method?

Nigel

JasonB20/02/2012 17:08:59
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On my Fowler traction engine there are six holes from each end to the valve slots, they start placed around a PCD and end up in a straight line.

I used trig to work out the angles and set the cylinder to suit using one of the little digital angle boxes, started the hole with a slot drill and then drilled through, turnd out OK as you can see here and here

J

Edited By JasonB on 20/02/2012 17:09:59

fizzy20/02/2012 18:15:38
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I just did mine..this way is very easy: I marked the exact route the drill needed to take on the outside of the casting. Put a 2mm dia lengtht of bar in the 2mm collet and lined the line on the casting up with the edge of the vertical bar, as in previous post. Swap bar for cutter and slightly relieve are where holes are to go - so the drill will now be cutting perpendicular to the face (square in other words, this way the drill goes in straight and true and comes out exactly where you expect it to!). Remark and pop the hole centres and drill away - near perfect results! I dont wurry about the holes being at slightly different heights in the ports (a result of the holes being druilled in parallel to the bore), never been a problem.

fizzy20/02/2012 18:15:40
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I just did mine..this way is very easy: I marked the exact route the drill needed to take on the outside of the casting. Put a 2mm dia lengtht of bar in the 2mm collet and lined the line on the casting up with the edge of the vertical bar, as in previous post. Swap bar for cutter and slightly relieve are where holes are to go - so the drill will now be cutting perpendicular to the face (square in other words, this way the drill goes in straight and true and comes out exactly where you expect it to!). Remark and pop the hole centres and drill away - near perfect results! I dont wurry about the holes being at slightly different heights in the ports (a result of the holes being druilled in parallel to the bore), never been a problem.

Tel20/02/2012 20:07:14
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Posted by nigel jones 2 on 20/02/2012 18:15:40:

I just did mine..this way is very easy: I marked the exact route the drill needed to take on the outside of the casting. Put a 2mm dia lengtht of bar in the 2mm collet and lined the line on the casting up with the edge of the vertical bar, as in previous post. Swap bar for cutter and slightly relieve are where holes are to go - so the drill will now be cutting perpendicular to the face (square in other words, this way the drill goes in straight and true and comes out exactly where you expect it to!). Remark and pop the hole centres and drill away - near perfect results! I dont wurry about the holes being at slightly different heights in the ports (a result of the holes being druilled in parallel to the bore), never been a problem.

As often as not I do 'em this way as well, tho the only marking I usually do is the starting point and the bottom of the port with a 'Sharpie' magic marker.

Stub Mandrel20/02/2012 21:41:32
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If you use a cheap tilting vice (they do have uses) hold the casting so the port is against the lower jaw and level with the top of it, you can set the angle and then wind the drill down and see that it is sufficiently far back from the jaw before bolting down the vice and replacing the casting. Mark teh depth of the hole on the drill too!

Neil

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