Math help with block
 

Check out Roolen's "Disapearign Pinwheel" tute at her blog http://www.roolen.blogspot.com/ You can get translation into English. Go into MC/Tutorial and scrool down until you get to "Disapearing Pinwheels" Such a great idea.!!!!

But What do you think the math would be to get certain size block. Any ideas? Maybe you should make block and then that is the size you have.

EG- If I want a 12" finished block I will need to make pinwheel block 13 1/2" unfinished to have block cut into 4 1/2" patches. But what size do you make the beginning pinwheel blocks. and is there a rule of thumb for use on any size block. HELp!!!!!

Her projects are certainly beautiful! Have you checked with the website Blocks Galore to find a similar block? That would definitely help with the math. Good luck!

Added thought after looking at pinwheel blocks on Quilt Blocks Galore website: I think your math is right on track. Hopefully others will have a better ideas.

Problem is that you have to cut the pinwheel block into 3 across and down and then you need to add 1/2" for seam allowance. Question is what size do you make the blocks for the HST pnwheels if you want an 13 1/2" unfinished block ? My brain is tired!!!!!

If you want to start with a 13.5" block, each of the 4 half square triangles will need to be 7 inches. So I would cut 8 inch squares, make the hst blocks, trim down a bit to 7". When you join the two 7" blocks, you loose a half inch in the seam (two 1/4" seams). The result is 13.5". Not sure what rule of thumb you are looking for. Something about the pinwheel block or the recut disappearing 9 patch??

The rule of thumb would be for calculations for ANY size block for both HST and especially the pinwheels. .

I agree - 8" would give you some wiggle room to nicely square up the HSTs to 7". Then you should be good to go to cut and re-arrange as you wish.

Take a look at this block it's a disappearing 4 patch which ends up with the pinwheel in the middle
http://www.quiltingboard.com/tutoria...ks-t68180.html

Take a look at this block it's a disappearing 4 patch which ends up with the pinwheel in the middle
http://www.quiltingboard.com/tutoria...ks-t68180.html

Incase your interested here is some more variations of blocks
http://freequiltpatterns.blogspot.ca...patch-and.html

Official calculation for HSTs is add 7/8" to the FINISHED size you are aiming for. Since most folks aren't into that 1/8" thing, the rule of thumb is cut your beginning square 1" larger than you want, then trim the resultant triangles down. Remember that your HSTs will measure 1/2" larger than your finished size. So if you want 6" FINISHED hsts, cut your squares 7", make your triangles, then trim them down to 6.5".
Pinwheel blocks are 4 HSTs, two in each direction. Decide what size FINISHED pinwheel you want, then divide that in half. This is the size of a FINISHED HST in your pinwheel, so just use the formula above.
So, for instance, you want a 6" pinwheel. Half of 6 is 3. Add 1" to the 3 and cut your starting squares 4", sew your triangles and trim to 3.5".

I am thinking the rule of thumb is for any block size is " finished block size + 1 1/2( this will allow for the cutting of the block into 3rds) : then size of block divided by 2 ( for HST) +1/2"= size of blocks to be cut for HST.

EG. If I want a 12" finished block - 12" + 1 1/2"= 13 1/2"( that is the size of the unfinished block to be made into pinwheels) To determine block size for HST 13 1/2" divided by 2= 6 3/4 then add 1/2 for sewing on diaginal. so block to be cut into HST is 7 1/4. I will try this soon to see if it works.

I think this way sound easier that making 2 blocks and then cutting and sewing them together. Also the 1st pic Roolen shows is with origianl block in pinwheel.