Problem with a model I am building

Hi all,
I am trying to build the Lady Stephanie beam engine, Vol 3 page 211 in Engineering in miniature.
I have started work on the Entablature but have come a little unstuck on the
wording for one of the holes. Can someone clear it up for me?
It says... 2.3mm Drill spotface for 8BA on top, 3/16" under.
I have checked the dimension of the drill for 8BA and it is 1.8. I am assuming spotcase is to put like a lead in (probably flat, though I don't have a flat drill).
Should I be drilling right through and with what? an 8BA tapping drill, do I need to tap the hole?
Something else that is confusing me on this drawing... it may be too much information here for what is needed...
4 holes tap 8BA 5/32" deep, stud 1 3/16" long. Do I need to know what the stud is? If so, what does that mean for the hole?
Thanks for your help. I have a little more work to do on this, so will check back shortly for any responses.
Best regards, Dave Colliver. http://www.AshfieldFOCUS.com ~~ Customise your internet experience http://www.FOCUSPortals.com/customise.asp
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sun, 6 Jun 2004 11:27:38 +0100, "Dave"

Spotface is usually meant to provide a flat surface for the bolt or nut, and only enough metal is removed to provide a suitable area for a flat seating.

Measure the diameter of the nut or bolt head or washer, and spotface 10 thou larger in diameter until you have a formed circle only, don't take it down deeper than is necessary to give a circular faced area.

Stud is presumably the same as the 8BA thread you are putting in.

Should get a few replies on this from the others who may be more technically able than you and I... :-))

Peter
-- Peter & Rita Forbes snipped-for-privacy@easynet.co.uk Engine pages for preservation info: http://www.oldengine.org/members/diesel
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Hi,
Thanks Peter, this is what I thought, but with the wording, made it a little unclear. Looks like I should spotface to 2.3mm then drill a hole all the way through for 8BA but 3/16" under??? Does that mean drill a 3/16" dia hole on the underside of the fixture or drill the spotface for 3/16"?
BTW. I was an apprentice trained precision mechanical and production engineer a number of years ago, but I came out of engineering to follow another career path (RAF) about 15 years ago. It is amazing how much you forget... but apart from that, the drawing is not too intuitive with the way it tries to describe the holes.
Best regards, Dave. ~~ Customise your internet experience http://www.FOCUSPortals.com/customise.asp

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sun, 6 Jun 2004 13:00:16 +0100, "Dave"

Difficult to interpret a drawing without seeing it :-)) I'm on our CAD computer at present, doing a large cabinet drawing for our metalbashers, and interpretation is the bane of drawers and readers alike.
If you have a scanner, scan the part you are unsure of and email it to me, that way I canb get a better feel for the problem.

I don't think you forget, but sometimes it can be a problem remembering the detail if you haven't used the knowledge for a while. Swapping between electronic and mechanical CAD packages gets my grey matter exercised sometimes!

Peter
-- Peter & Rita Forbes snipped-for-privacy@easynet.co.uk Engine pages for preservation info: http://www.oldengine.org/members/diesel
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sun, 6 Jun 2004 11:27:38 +0100, "Dave"

Without having the drawing to hand this is my interpretation of it.
Drill through 2.3mm, spot face on top to suit 8BA and spot face on the bottom 3/16" [possibly for a washer and nut ]
A spot face is a flat slightly recessed surface for a washer or bolt head to sit, you usually go just deep enough to clean up and form a slight recess.
Reasoning behind this. If t was a tapped hole you wouldn't need a bottom spot face and the drawing would say tap as in the later example you have posted. If it was a blind hole, again no need for a lower spot face and it would have a depth.
Is there a General Arrangement drawing [ GA ] that shows what goes thru this hole?

Drill 4 holes with an 8BA tapping drill 5/32" deep and tap, Fit an 8BA stud into the hole that's 1 3/16" long over all. Again does the GA show any of this ?
You often have to piece this together on drawings by adding various dimensions up.
Hope this helps.

-- Regards,
John Stevenson Nottingham, England.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Hi,
Thanks John and Peter,
(Whoops John, I clicked reply, which replied direct to you rather than reply to group, so I have just copied to group now.)
I have looked further through the series to see what it is...
In vol 4, page 147, there is a drawing which shows this hole in use, but it is still not quite clear. Page 148 shows the actual item. This is a control shaft pedestals. These look like they support a shaft just underneath the entablature.
The assembly drawing shows that there is a nut on the top side, the pedestal underneath, shoving through, so I guess Johns interpretation is correct. Drill large enough for 8ba to pass through (2.3mm) and mark the top and bottom surface, top large enough for a mating surface for a nut and bottom 3/16 which is the diameter of the pedestal mating surface.
As I don't yet have any 8ba nuts or the shaft yet, I will leave this hole un drilled, though I have put a mark in place with a center drill so that I can easily return to it later.
Thanks. Dave Colliver.
BTW. John, whereabouts in Notts are you? I am in Kirkby-in-Ashfield. ~~ Customise your internet experience http://www.FOCUSPortals.com/customise.asp
wrote:

the
do I

stud
check
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

just
I worked out that the stud must be 8BA, what I meant when I was asking is why do I need to know what length the stud is, at this stage, after all, I am only drilling and tapping an 8BA. The stud length is irrelevant as far as I can see, so why put it on the drawing, unless there is a meaning to it. (With the drawing I have got, there is no meaning to it.)
Regards, Dave.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sun, 6 Jun 2004 17:35:06 +0100, "Dave"

Guessing ?? Possibly because the stud isn't on the drawings as a separate item ??
Dave, I'm 2 junctions down the motorway at long Eaton
-- Regards,
John Stevenson Nottingham, England.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.