Glass dimensions, 1926-27 Roadster?

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ArthurB
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Glass dimensions, 1926-27 Roadster?

Post by ArthurB » Wed Mar 27, 2019 9:59 pm

Does anyone just happen to have an Autocad file or a scale template drawing file for the glass in a 1926-27 Roadster? I have the dimensioned drawing from an old thread ( http://www.mtfca.com/discus/messages/29 ... 1201254336 ) but if someone's done the work to bring this into modern manufacturing it will save me some time.

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Re: Glass dimensions, 1926-27 Roadster?

Post by Mark Nunn » Thu Mar 28, 2019 8:34 am

I don't have drawings but I will make them. Did you confirm that the drawings on the other post have the correct part numbers? I suspect the glass that was cut for my car in the 1990's is tempered. I don't see a layered appearance on exposed edges. I will repost here when it's ready.


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Re: Glass dimensions, 1926-27 Roadster?

Post by Original Smith » Thu Mar 28, 2019 10:46 am

Get the Ford glass book. It has everything.

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Re: Glass dimensions, 1926-27 Roadster?

Post by ArthurB » Thu Mar 28, 2019 11:07 am

The part numbers and drawings come from the 1927 Ford Glass Price List (attached). I'm trusting it is accurate. My understanding is that where there are pairs of numbers, it represents the min/max spec for the overall assembly.
1927glass.pdf
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Re: Glass dimensions, 1926-27 Roadster?

Post by Mark Nunn » Thu Mar 28, 2019 12:43 pm

I've started on a drawing of G-1C 40308. I cannot tell what one of the dimensions is showing. This is on page 3. What is the 8 25/32" 8 27/32" dimension for? Is there a horizontal flat at the corner? Is the 2 3/64" dimension to an intersection of the two arcs that is not an edge of the glass?

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Re: Glass dimensions, 1926-27 Roadster?

Post by ArthurB » Thu Mar 28, 2019 6:35 pm

Mark, I think I can explain the vertical dimensions. It is discussed in second to last post at the old discussion thread linked above, but here is my "simplified" view of it:

The drawing says at the middle of the windshield the vertical dimension is min 6 29/32, max 6 31/32. At the edges, measured against the vertical, it is min 6 29/32 + 2 3/64= 8 61/64, and max 6 31/32 + 2 3/64 = 9 1/64. BUT there is a 3/16" 45 degree chamfer at the top, so measured from the bottom of the top corner chamfer that vertical dimension is min 8 25/32, max 8 27/32. For some reason they shifted they projection of the chamfer to the bottom instead of the top, maybe so all the reference lines are relative to the horizontal datum of the top of the piece. Note that min 8 25/32 + 3/16 chamfer = 8 62/64 instead of 8 61/64, but the chamfer really doesn't measure 3/16" in the vertical, since that edge of the glass is not perpendicular to the top edge. The vertical distance from the horizontal top line to the lower corner of the chamfer will be slightly less that 3/16" because the glass bends inwards. I bet if we did the math to calculate the angle of the bend we would find that a 3/16" chamfer in the horizontal, when it intersects the almost vertical edge of the glass, measures 1/64" less in the vertical, or 11/64". 8 25/32 + 11/64 = 8 61/64, so it checks out!

Make sense? I can only imagine how many engineers over the decades have asked the same question about why the draftsman decided to call out the dimensions that way.

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Re: Glass dimensions, 1926-27 Roadster?

Post by Mark Nunn » Fri Mar 29, 2019 12:59 pm

Here is G-1C aka 40308. You can check my dimensions before I let this into the public. The original drawing was probably made using spline curve templates. Some CNC machine software does not accept splines. Therefore, I made the curves using the dimensions as datum points and then drew individual arcs between them. I made the arcs parametric where each end was tangent to the adjacent arc. I mention this because the curve at the bottom of the windshield has one connection that is not tangent. That is at the 1/32" point (4" from centerline). I suspect that the 7/64" dimension is a little short of actual, by about .005". I doubt that would adversely affect windshield fit so I didn't fuss with it. G-2C is next.
G-1C 40308.pdf
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Re: Glass dimensions, 1926-27 Roadster?

Post by ArthurB » Fri Mar 29, 2019 1:06 pm

My windshield frame arrives this afternoon so I will hand check the numbers then print the curvy parts and see how well they fit the frame. Thanks!

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Re: Glass dimensions, 1926-27 Roadster?

Post by Mark Nunn » Fri Mar 29, 2019 2:20 pm

Arthur, this drawing may make measuring easier. I added vertical dimensions to the top edge of the glass.
G-1C 40308 half.pdf
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Re: Glass dimensions, 1926-27 Roadster?

Post by ArthurB » Tue Apr 02, 2019 1:54 pm

I printed the drawing and used it to cut a half template. My windshield frame is a reproduction from Speedway Motors (says "Mr. Roadster" on the box). The quality looks very good to me, though I don't have an original to compare it with. The welds certainly look good.

When I insert the template all the way into frame, it settles on the bottom curve of the frame pretty well. All the contact is within 1/16" or less. The template top is exactly flush with the top of the metal on one side, maybe 1/16" high on the other. This doesn't include any room for the glass setting tape, but I see from Lang's the tape is only .013" thick which is within the tolerances of my scissor work. I am assuming we want this to be flush to work with the glass clamp.

The sides don't look quite as good. The first contact is at the top edge. When the top is in contact, the mid point looks about 1/8" or maybe even 3/16" short, and the bottom is about 1/8" short.

My frame measures 37 1/4" at the top, compared to the 37 7/16" glass measurement in the drawing. The frame does have a little flex in that dimension, but it does seem like a tight fit. Does anyone else have a frame to measure? I've never assembled one of these before so I don't know if a real tight fit is a benefit or a problem. It seems like if I stretch the frame outward at the top I would be able to get glass cut to this template to fit-- a tight fit, but then the curvature of the side would probably match a bit better too. It also seems like shaving up to 1/8" off the width a the top (each side) would make for a comfortable or looser fit.

Hoping someone with experience assembling windshield glass can weigh in on how tight a fit is optimal. Remember this is a 26/27 frame, so there is no glass channel. I believe it is assembled with the tape rather than the silicone.

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Re: Glass dimensions, 1926-27 Roadster?

Post by Mark Nunn » Tue Apr 02, 2019 3:28 pm

Do you have the upper frame too? Is the inside dimension set for 37 7/16" glass?

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Re: Glass dimensions, 1926-27 Roadster?

Post by ArthurB » Tue Apr 02, 2019 3:59 pm

Good question. The top and the bottom line up perfectly with no stretching, so I don't think I would want to stretch the bottom to fit the glass or it won't match the top. The top is nice and square. I measured more carefully and it looks like the top glass channel measures 37 3/16", so I think the maximum width of the glass to fit it would be 37 1/8", and that would be a tight fit.

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