What type of frame are you trying to make? If it's a stretcher they are best with very specific joints which require a special router blade to cut. You can make frames that don't 'rack' under tension but they need to be pretty thick. Stretchers normally have a rounded edge so the tensioned canvas doesn't touch the stretcher bar.
Tried to find an example on the Trend site but failed. Have a look at the end of commercial stretcher bars. There are other ways but commercial stretchers are the sweet spot.
What type of frame are you trying to make? If it's a stretcher they are best with very specific joints which require a special router blade to cut. You can make frames that don't 'rack' under tension but they need to be pretty thick. Stretchers normally have a rounded edge so the tensioned canvas doesn't touch the stretcher bar.