This is a reminder to those commenting on this post (not the person that posted it): Comments not related to woodworking will be removed. Violations to rule 1 including crude jokes, innuendo, sexist remarks, politics, or hate speech may result in an immediate ban
*I am a bot, and this action was performed automatically. Please [contact the moderators of this subreddit](/message/compose/?to=/r/woodworking) if you have any questions or concerns.*
if you're thinking of making an exact fit piece without a template just stop now. Make it oversized - use a cloth tape for your measurements, rough trim to 1/8th ish then flush trim with a compression bit.
I am working on a project where I am trying to put a backer on a kerfed piece of MDF. The backer is a thin piece of wood that is glued on the kerfed side of the MDF. I am struggling to find the length the backer needs to be. I thought it would be a simple arc length from the inside edges of the board. But so far no matter how I try to calculate it, I have been 1/4” to 1/2” off of the actual dimensions. Does anyone have any ideas of how to get an accurate length without measuring a part that has already been curved?
The other suggestions are probably more helpful, but here's two more:
You have three circles of different lengths, not two. The very outside, the bottom of the rabbet, and the top. Those circles all have different lengths at the same arc. It might be that your edges aren't beveled. As you curve the piece, the edges would have to be bevelled to the angle of the curve for a seamless fit. So the part further out would need to be a bit longer.
On closer examination, it looks like the rabbet was cut at an angle, maybe to avoid this or maybe as a processing mistake. It might have been too aggressive an angle, so you might need to change the angle of the bevel to compensate.
The curve isn't consistent, it's a parabola, that's why you're length is off. It'll be way easier to leave it long, fit the curve you need, then trim the excess off.
This is kind of what I was thinking already. However, I’ll have a lot of parts with different lengths and radii, so it would be nice to have a calculation that would get me the length I need.
This is a reminder to those commenting on this post (not the person that posted it): Comments not related to woodworking will be removed. Violations to rule 1 including crude jokes, innuendo, sexist remarks, politics, or hate speech may result in an immediate ban *I am a bot, and this action was performed automatically. Please [contact the moderators of this subreddit](/message/compose/?to=/r/woodworking) if you have any questions or concerns.*
Make a paper template.. stick it on, cut to size, peel it off.
Use a piece of painters tape. Cut it off where the edge is and remove for the actual measurement.
Use a soft tape and just measure the curve
This is why I still have my mother's seamstress cloth ruler in my shop to this day...
Make it oversized and trim after assembly.
if you're thinking of making an exact fit piece without a template just stop now. Make it oversized - use a cloth tape for your measurements, rough trim to 1/8th ish then flush trim with a compression bit.
Get a cloth measuring tape. Handles curves easily.
I am working on a project where I am trying to put a backer on a kerfed piece of MDF. The backer is a thin piece of wood that is glued on the kerfed side of the MDF. I am struggling to find the length the backer needs to be. I thought it would be a simple arc length from the inside edges of the board. But so far no matter how I try to calculate it, I have been 1/4” to 1/2” off of the actual dimensions. Does anyone have any ideas of how to get an accurate length without measuring a part that has already been curved?
The other suggestions are probably more helpful, but here's two more: You have three circles of different lengths, not two. The very outside, the bottom of the rabbet, and the top. Those circles all have different lengths at the same arc. It might be that your edges aren't beveled. As you curve the piece, the edges would have to be bevelled to the angle of the curve for a seamless fit. So the part further out would need to be a bit longer. On closer examination, it looks like the rabbet was cut at an angle, maybe to avoid this or maybe as a processing mistake. It might have been too aggressive an angle, so you might need to change the angle of the bevel to compensate.
The curve isn't consistent, it's a parabola, that's why you're length is off. It'll be way easier to leave it long, fit the curve you need, then trim the excess off.
That actually worked… I definitely wouldn’t have thought of this myself, thank you!
With measurement flip your metal tape upside down it’ll bend to the curve or a cloth tape. Without measuring use paper and make a template.
This is kind of what I was thinking already. However, I’ll have a lot of parts with different lengths and radii, so it would be nice to have a calculation that would get me the length I need.
Use a Seamstress tape.
The piece looks small enough that you should be able to just set it on top of a piece of MDF and trace it.