Router guide bushing ?

[Brian Runau]

I'm working on cutting a mortise using a jig and my router. The set up calls for a 30mm guide bushing and a 3/8" spiral bit. I have a Freud router and their bushing kit. I have the adapter for the bottom of the router that accepts the guide bushings. The 30mm dimensional reference is to the OD on the extension that runs inside the jig? Largest guide bushing in my kit is less than 1".

Thanks.

Brian

[Jamie Buxton]

Maybe this fits your router:? https://www.amazon.com/Trend-US-30-Screw-style/dp/B00382UOGM/ref=pd_sbs_469_t_0/143-6056759-3319969?_encoding=UTF8&pd_rd_i=B00382UOGM&pd_rd_r=a59b27a6-e42f-42af-8f18-01721f4bd030&pd_rd_w=F75A2&pd_rd_wg=Ncjzl&pf_rd_p=5cfcfe89-300f-47d2-b1ad-a4e27203a02a&pf_rd_r=1N290T66T2Q9APC33KE0&psc=1&refRID=1N290T66T2Q9APC33KE0

[Brian Runau]

Jamie:

I have that in my kit. I can't figure out what size busing to use with the jig. Let me try and figure it out by math and see if I can do that by the process of elimination. Thanks. Brian

[Eric Schmid]

It sounds like the jig maker is telling you which size (both but and bushing) to use for a specific mortise width. Is that correct?

Your question appears to be regarding the ID or OD of the guide bushing. I can’t think of a reason why the ID matters in your case, as long as the 3/8” bit has sufficient space inside.

I always test on scrap of equal dimension. A shallow mortise will do, just enough I can get a caliper in the opening and on the cheeks.

[Brian Runau]

I see now this was a basic question, but you don't know what you don't know. Old and tired today, "Thick as a Brick" musical reference to a group Jethro Tull. Band from the 70's for you young'uns. The 30mm guide busing has a 3/4" od and this is correct for the jig. thanks. brian

[Brian Runau]

The hole size is too large for the tenon in the sample I ran. See attached instructions. 30mm guide bushing and a 3/8 straight bit are what it calls out. left a mortise in the sample piece that was too wide and too long. The OD of the bushing that fits into the jig was 3/4" dia. Do they make a guide busing that has a 30mm OD that fits into the slot on the jig? See instruction page attached. Thanks. Brian

[Edwin Santos]

The hole size is too large for the tenon in the sample I ran. See attached instructions. 30mm guide bushing and a 3/8 straight bit are what it calls out. left a mortise in the sample piece that was too wide and too long. The OD of the bushing that fits into the jig was 3/4" dia. Do they make a guide busing that has a 30mm OD that fits into the slot on the jig? See instruction page attached. Thanks. Brian

You could try wrapping masking tape around the outside of the bushing as a way of making it larger. In this way you can sneak up on the correct size by making test cuts and adding masking tape as needed. I have done this many times to fine tune cut-outs and mortises.

Or you could adjust the size of your jig by making the opening smaller. You're basically juggling three variables; bit size, bushing OD and jig hole size. Playing around with any or all of these variables will influence the mortise size.
Edwin

[Brian Runau]

Edwin:

So the instructions are not correct? Thanks. Brian

[Eric Schmid]

You can get the specified guide bushing size, adjust the tenon, rework the math, or some combination of these. What is the resulting mortise size supposed to be according to your plan using the combination they recommend? What is the mortise size of your test piece?

Also, do you have a guide bushing with an OD closer to 30mm (between 1" & 1 1/8")?

[Edwin Santos]

Edwin:

So the instructions are not correct? Thanks. Brian

What size should the mortise be for the fit to be correct? Your post above says the sample mortise was too wide and too long. What dimension do you want, and what dimension was your sample?

I am thinking the instructions are correct, but your sample mortise was off because you are using a 3/4" OD bushing instead of a 30mm OD bushing.

Was your mortise off (too big) by 7/16" in each dimension?
Then again, maybe I don't understand the issue you are having.

Edwin

[Steve Fish]

I think you’re right Edwin. I thought 30mm was around 1-3/16”. 19/32 from center vs 12/32 (3/4” bush). You need come in 7/32 on every side if my math is correct.
I’m not understanding why a metric bushing was used either

[Edwin Santos]

I think you’re right Edwin. I thought 30mm was around 1-3/16”. 19/32 from center vs 12/32 (3/4” bush). You need come in 7/32 on every side if my math is correct.
I’m not understanding why a metric bushing was used either

Steve,
If you and I are right, then the solution is to either (i) find a 30mm OD bushing or better yet (ii) resize the jig opening by 7/32" on each side (7/16" overall) taking care to keep the centerlines located per the plan, and then use the 3/4" bushing.

I too wonder why the author is using a non-standard bushing like that. After all the PC type bushings sit in a 1 3/8" counterbore so even if the OP finds a 30mm bushing, I'm not certain how it would mount.

Maybe the author is from the UK or Europe where a bushing like that is typical?

[Brian Runau]

Edwin:

Plans are from fine woodworking. Brian

[Edwin Santos]

Brian,
If you want to follow the plan exactly, Amazon has a 30mm screw on guide bushing for $16.65: https://www.amazon.com/Trend-US-30-Screw-style/dp/B00382UOGM/ref=sr_1_10?keywords=30mm+router+guide+bushing&qid=1583244511&sr=8-10
Edwin