Ok here we go...PMF!

[Sheddie]

Can you put on another photo with with a hunk of ply or something clamped on the back with some lines on it to give us an idea of what you are thinking. Would also be good if you can get the photo from square on.
As for the front curve, I quit like the other line you have drawn on it, but that is probably governed by what you are looking to do with cabinets inside.

[dales133]

Yea I'll take a couple tomorrw

[KCStudly]

19 mm is true 3/4 inch. Which is a lot by accuracy standards in my book. Likely enough to catch your eye at the would be tangent point if the center is off that much.

Not sure what the problem is at this point (better more complete pictures will help), but one thing you can do is double check your center point and radius.

Did you use a hard trammel to trace your radius or the string method (string can stretch or the marker can tilt)?

Or is it a problem due to cutting the radius before joining the panels? (Better to join before doing the final finish cut.)

[dales133]

Yea it's after joining the panels I was struggling to get the 19 inch radius flowing into the 48 inch radius.
Even though I'd changed the 48 inch to 100mm it still didn't matter where I positioned my center it still didn't mate up looking right.
I used an aluminium T square as the compas

[Sheddie]

What I found that worked really well as a compass was a strip of thin mdf. I drilled a small hole in one end and screwed it to the wall panel at the pivot point, then drilled a snug hole for the pencil at the radius and perfect arc.

[dales133]

Yea i made one yesterday.ive got no issue with the accuracy as far as my outlines concerned but more marrying the two radius together

[Sheddie]

I just checked on a piece of paper with my old school compass. First draw the large arc, then set your pencil on the transition point where you want to change to the smaller arc, the pivot point needs to be at right angle from this point.

[dales133]

I'll post up a pic later on.
Pain in the arse having to do it from the computer just to add pics

[KCStudly]

It sounds like you are talking about the larger top radius of your hatch where it transitions into a smaller radius at the back or bottom of the rear of your profile. Just thumbed thru your build again and don't see where you posted a profile sketch or layout, so can't be sure.

If so, the center point of the smaller radius has to be on the radial line of the larger radius at the tangent point of the two arcs, otherwise there will not be a smooth transition.

You might be able to cheat it a little by sanding the two sides together, but not a lot without creating a third curve or flat spot.

Strike a straight line from the point where you expect the two curves to meet thru the center point of the larger curve and see if the center point of the smaller radius is close to landing on the line.

If you are still struggling with it come Monday, post up some more specific info and I can layout something more detailed for you.

[dales133]

Yes kc that's the issue exactly.
The problem is I have nothing but a small ruler in inches and no sketchup plan and it's wider and longer than the generic benroy so all of these factors bring thier issues

[KCStudly]

Use the ruler to transfer measurements to a longer stick; a makeshift story pole or trammel. When marking, don't use the ends of the ruler; lead an inch reading from the graduated marks on the side of the ruler (errors at the end of the ruler add up and your eye can pick a marked line much easier then a dull imprecise end... just be sure to always add the extra inch back on the other end of your measurement... harder than it sounds sometimes).

Assuming that your 19 inch radius center point is tangent to the bottom and back of your sheet (i.e. 19 inches above the bottom and 19 inches forward of the rear), your 48 inch radius is centered on the bottom edge of your sheet, and there is no flat line between the arcs (i.e. one radius flows into the other in a continuous tangential spline) using Pythagoras, the center of the large radius should be about 40-15/16 inch forward from the original rear edge of the sheet.

48 - 19 = 29
This is the hypotenuse of the right triangle that is defined by: the center of the 48 inch radius; the center of the 19 inch radius; the base line; and the vertical perpendicular leg between the center of the 19 inch radius and the base line.

sq root of (29 squared - 19 squared) + 19 = 40.9 inches
This is the base of the above described triangle (the sq root of the hypotenuse sq'd minus the opposite side sq'd) plus the offset from the rear of the original 19 inch radius' center along the horizontal baseline.

Clear as mud, right?

So if you draw a point 19 inches up and 19 inches back; then draw a point 40.9 inches back along the base; then draw a straight line between the two extending 19 inches past the small center; the two arcs will meet at that point; and the 19 inch radius will touch the bottom and back of the sheet tangentially.

Hope this is what you are intending, that my math and mental picture of the scenario are correct, and that it some how helps to solve your problem.

[dales133]

Yea that's clear I just hate imperial fractions and I stupidly started framing and tried 50 mm off the bottom of the sheet witch took off the center or the compas point for the larger 48 inch radius.
My reasoning was my door cutouts would suffice for the extra length I needed without having to get a 3rd sheet but I'm starting to regret that decision

[Plainsgirl]

You haven't lost your mojo, have you? I'm following your build VERY closely Don't let miscalcs get in the way of this awesome project!
Kerry

[Sheddie]

You haven't lost your mojo, have you? I'm following your build VERY closely Don't let miscalcs get in the way of this awesome project!
Kerry

You tell him Kerry.

[dales133]

Nah I haven't lost my mojo just been misbehaving at a blues festival.
Great little local blues club puts it on and would be perfect for the TD next year.loads of caravans and camper trailers there last night.