Alternative to 5/8″ spiral uncut bit
tom93311
| Posted in Jigs, Fixtures, Tips & Tricks on
I am going to make the Morley Mortiser as featured in latest issue. For the top piece that accepts a guided bushing I need to rout a 5/8″ slot using shallow successive passes on 3/4 BB plywood with stops set up to limit the travel of the piece over the router.
Can I do this instead with a straight bit? I cannot find a 5/8 spiral bit for less than $129.99. This is simply too much money for one time use to make a jig. Any suggestions would be appreciated.
Replies
Yes, you can.
There are many ways - the easy way to do this is to make some 5/8" thick stock. Cut down the length of your work. Glue in the 5/8" stock leaving the slot you need.
If you are wedded to the router:
- If you have a pattern bit:
Make a pattern using the technique above then use that to guide your pattern bit.
- assuming a more common half inch bit:
In a router table:
If your slot is central in a piece -
Using a scrap piece the same width, centre the bit as best you can on the piece. Cut a slot from both sides of the piece - measure the slot. Increase distance between fence and bit until your slot is 5/8". remember that you will double any difference as you will cut from both sides.- cut your actual work.
If your slot is not central in a piece:
Create a 1/8" shim.
Cut your first slot with the shim against the fence, aligning with the edge nearest to the fence.
Remove the shim
Complete the cut.
(Doing it this way, cutting the far piece last avoids a climb cut)
You can also do this with similar techniques and the router above the work with an edge guide.
If you already own a ⅜" or ½" upspiral I would use that first then make a final pass with the ⅝" straight bit. This reduces the load on the straight bit and eliminates the heat causing chip clearing problems of using a straight bit. None of your setups would need to be changed as the larger bit would automatically be centered.
There is one factor you would need to account for, your start and end points, make sure your set them up for the ⅝" bit. If you do this the passes with the smaller bit will be slightly short but it will be corrected when you make the pass with the larger bit.
Yes you can, by drilling a 5/8 hole at both ends of the slot you can do it with successive passes with a 5/8 straight bit. If all you have is a 1/2 bit you could do it the same way, but move the guide 1/8 away once you have cut through the plywood.
Good suggestions above.
Use what you have. It's a jig, right? It doesn't need to be pretty.
I post pretty much the same comment here as I did in the online extra section.
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Regarding the morticer, not to critizice it but in my opinion it's better to instead make it with a fixed top and using it with dual fences on the router, referencing the long sides of the jigs top, Pat Warner style https://www.portercalls.com/Images2018/PatWarnerMortiseJig4.jpg
...my take on Warners jig, with integrated clamps, also in video below. https://pin.it/128c1Ni
Less complicated build without moving parts or a slot that needs to be dead on matching your guide bushing during the jigs entire lifetime. Less flex in the construction since top is fixed, bigger hole down in the jig to see your layout lines and whats going on. Length stops can be set using layout lines rather than making a custom spacer block for each joint. You can use direct layout from the tenons rather than the center of them. Also double tenons can be done in the same run having the spacer between the fence and the top plate and move it from one side to the other without even switching off the router. Double mortice with this teqnique shown at 5.15 and forward here https://youtu.be/KBoim06Hmyg
thank you for the suggestions. I don’t have much experience with routing plywood so I was not sure how it would act with the different bit styles - these ideas give me a lot of different options to consider so thank you. Ola’s jig is a nice piece of engineering. Thanks for the links and info.
Could try using a 5/8" straight bit w/ boring point from Whiteside. The bit has an added carbide cutter to help clear out the center.
https://www.whitesiderouterbits.com/products/1076F
If you have a router table with a lift, here is a simple mortice sled that works well. https://youtu.be/GyyMiuB62-k
A straight bit works just fine. Keep in mind spiral bits are a relatively new innovation so there is always a way to make a cut without them.
This cut is really simple though. Just set your router table fence up with some stop blocks and carefully lower the piece onto the bit. 3/4 is a big cut so do it in stages, maybe 1/8-1/4" at a time, slowly raising the bit with each cut.
A straight bit should honestly be better for plywood than an upcut.
Upcuts tear upwards and are basically the worst choice for ply 😅
A downcut would also be good, or a compression bit if you have a set up that allows you to cut deeper than the upcuts on the compression in one pass, (but if you're working it by hand you probably don't have this).