R Rhodes

Daphne mezereum

OK. This will be my last post on this topic.

The OP stated that he wants a 30 foot width frame.  He built a jig to give a 15 foot radius.  The ONLY way a 15 foot radius will make a 30 foot diameter is to complete a  SEMI-CIRCLE.  Not a semi-OVAL like in your drawings.  If you want a low ceiling, arch top frame, you have to change the radius of your bends to target a much wider diameter and then not complete the semi-circle and lose height along the sides, or install knee-walls resulting in higher center height.

Your diagram is NOT a complete bend to the jig of the entire length of the rails as would be need to get to 30 feet width.  It is over bent on the ends and almost no bend at the "ridge".  While this is a very desirable shape for a low height greenhouse, it is NOT the result of a complete, simple, semi-circle bend of a top rail hoop frame bender, by default.

Not sure what you are trying to accomplish with your somewhat confrontational replies, but I just had my 7-year-old proof the content of my previous replies, and the instruction is spot on.  I'm signing off and going back to actually BUILDING greenhouses.  It's one of the many things I DO.

(Pi×D)/2...

R Jay wrote:
Hi Roger

I suspect that there was only one bend at the 12-foot mark and it went too far--giving the
10.6ft height and 41 foot width

Gradual bends along the 24-foot length--and using your suggestion of going slightly
past so it springs back--will give a 15-foot height and 30-foot width

My assumption was a continuous bend the full length based on his description of how he designed the bender.

R Jay wrote:

Using those results, you are only getting a finished height of 10.6 feet. You need to keep your current jig but pull your bending a little past
so it springs back to the radius. Until you have a 15 foot height you'll be long on the width.

If the pipes have been bent so that the total width is 41 feet with a height of 10.6 feet, then the pipes were bent too far to start with.

Not if he wants a finished width of 30 feet....

Andrew Roesner wrote:Hi All!

I am in the midst of building my own hoop house. it's 30' wide and 95' long. The many "build your own greenhouse" websites that sell hoop benders don't make a 30' bender so I'm making my own. The first version is a 4'x 8' sheet of plywood cut in half length wise and screwed together. I stretched some masonline out to a 15' radius and traced the arc on the plywood. I used the cut out from that to add a 3rd ply in the middle of the two sheets and set it back about a half inch so the there is a groove where the hoop can rest while bending.

I gave it a try on saturday and everything works fine, except the hoops do not form a 30' diameter. not even close. I'm using 2 24' lengths of 1 5/8" top rail to create the hoop. the obvious answer is that the hoops snap back a bit after bending and so I'm guessing the radius of the bender needs to be less than 15'. the question is, HOW MUCH LESS!?! the approximate diameter when the hoops are assembled on the ground was 41'. I know that the diameter when assembled should be a foot or two wider so that the hoops will have some tension when setting them, but this is too much.

does anyone have a suggestion of what radius to try to achieve my desired 30' diameter. is there maybe an equation? i've looked quite a bit but i've not found anything on the interwebs. does anyone have a link to point me in the right direction??

I found a website that mentions a 10% spring back which means i might want a 13.5' radius. I'd hate to cut a new radius and end up with it too narrow!

Thanks for the help!

Using those results, you are only getting a finished height of 10.6 feet. You need to keep your current jig but pull your bending a little past so it springs back to the radius. Until you have a 15 foot height you'll be long on the width.

Might take a look at bluestem.

The hardest concept I've ever had to make myself really embrace:


Every injury is preventable.

Installed a swale along the topside of the area. It includes fruit trees and support guilds. Still finishing the full design. The small garden this year was highly productive and well received. There should be a large permaculture demonstration garden with walking paths and community education components by next growing season.

A pic of the swale right after planting the 3 anchor trees.