This arch is built with segments and splines for strength Then a simple shopbuilt jig is used for assembly arid routing the arch

NOTE: Use more segments, not wider ones, to minimize waste on large arches p

■ utting an arch for a project (like ^^ the full-length mirror) can be an interesting challenge. You may think the easiest way to do this is to find a piece of stock wide and flat enough for the size you need, see Fig. 1. But there are a couple problems.

The first problem is waste. You end up throwing away a lot of wood after the arch is cut free. The other problem has to do with grain direction. No matter how you lay out the arch, some part of it will be held together by weak cross grain.

Thaf s why I make an arch in pieces (segments). Since you're gluing segments end-to-end, there's no weak cross grain to worry about And waste is kept to a minimum.

number of pieces. So how many segments do you need? Well it depends on the size of the arch. Three or four are enough for most projects. But the bigger the arch the more segments that are needed if you plan on keeping waste to a minimum, see Fig. 2.

weak point. However, there's an Achilles' heel to segmented arches. The pieces are glued together end

Waste

Segment grain to end grain — a pretty weak joint Fortunately, there's an easy solution to this problem. I just install a spline to strengthen the joint.

cutting angles. The key to making a segmented arch is cutting the angles accurately. A slight error compounds itself each time you make a cut. So what angle do I use? It depends on the number of pieces used in the arch, see Fig. 2. To find the angle, divide the number of segments into 180° (half of a circle). On the mirror arch the angle was 60° for three segments.

setup. For accuracy, I set the miter gauge with a protractor to make sure

Waste

Cross grain is weakest part of arch

Cutting an arch from a single piece of stock is wasteful

Waste if s right on. I also add a stop block to an auxiliary miter gauge fence. This way, all the pieces will come out the same length, see Figs. 3 and 3a. Note: Keep a couple of the waste pieces from the segment ends. You can use them later in an assembly jig.

slots & splines. Once the segments are cut to size, the next step is cutting a slot in the end of each piece to hold a spline. To center the slot, I flip the segments between passes on the table saw. (For the mirror the slot was W-wide x ^"-deep.) Now a spline can be cut to fit snug in the slot

The key to cutting splines is making sure the grain direction of the spline runs perpendicular to the joint line. To do this, I cut them out of the end of a scrap piece of hardwood, for more on this refer to page 28.

assembly. With the splines cut, the arch can be glued together. But trying to glue and clamp these angled pieces together is like trying to read a doctor's handwriting on a prescription — nearly impossible. So I use a shop-made jig, see Fig. 4.

This is a multi-purpose jig. Ifs an assembly jig where a single clamp on a three segment arch pulls the segments together. And once the pieces have been glued-up, it also holds them so a router can cut out the arch.

routing the arch. To cut the arch, I used a router and a 1/4" straight bit, refer to Figs. 6 and 6a. But first you'll need to attach a trammel to the router to guide it through the arc.

There's really nothing to making a trammel. Ifs just a piece of W-thick

NOTE: Use waste pieces on jig to keep segments from moving outward when clamping arch

Pivot pin is centered on width of jig

NOTE: Use waste pieces on jig to keep segments from moving outward when clamping arch

Pivot pin is centered on width of jig hardboard wide enough for your router base and long enough for the longest radius, see Fig. 5. Plus a couple pivot holes are drilled at one end.

One pivot hole is for the inside radius of your arch, while the other is for the outside radius. One way to check if the holes are in the correct location is to measure the distance between them. It should equal the width of your arch plus the diameter of the router bit. 03

NOTE: Keep waste piece for later use

NOTE: Keep waste piece for later use

ROUTER TRAMMEL

- hardboard radius of arch

» Outside radius 1A"-dia. f of arch

NOTE:

Width of trammel cut wide enough for base of router

Trammel is moved to second pivot hole to rout outside of arch

NOTE: Make multiple passes to rout arch

NOTE: Use carpet tape to hold arch securely to the jig

NOTE: Make multiple passes to rout arch

NOTE: Use carpet tape to hold arch securely to the jig

Trammel is moved to second pivot hole to rout outside of arch

k This adjustable mortis-ingjig can be clamped quickly to a workpiece.

Mortising Jig

Recently, Mike Wagner from Appleton, Wisconsin, sent in a video to us showing a mortising jig he had built. Ifs designed to work with your router so you can quickly knock out a bunch of mortises all cut to the same size and shape.

design. His jig is basically a "corral" for your router. The router rides on a MDF (medium density fiberboard) platform with guide strips screwed to the top. These strips keep the router centered over your workpiece as it slides back and forth routing the mortise, see Figs. 1 and la.

using the jig. This jig is designed to eliminate the lengthy setup time that's normally needed to rout a number of mortises. The way it works is a pair of adjustable fences are attached to the bottom of the router platform. Simply adjust one fence until the router sits perfectly centered over the workpiece. Then tighten the knobs so this fence can be used as a fixed fence. You won't need to move it again unless you switch to a different thickness of stock

To set the mortise length, start by marking the location on the work-piece. Then set the router in the jig against the fixed stop and slide the jig along the workpiece until the router bit lines up with your first lay out line, see Fig. 2. Now clamp the jig in place and set the adjustable stop, see photo above. To do this, move the router until the bit is aligned with the second layout line and lock the stop in place.

Once the length is set, you only need to align the jig with a single layout line for each mortise.

Shop Note: I like to use an upcut spiral router bit to rout mortises. It pulls the chips out of the hole. M

k This adjustable mortis-ingjig can be clamped quickly to a workpiece.

Guide

Adjustable

NOTE:

Distance between router guides equals width of router base

Fixed stop

Washer

Guide strip

VSxVA" machine screw

carriage bolt

Router platform

Adjustable fence

NOTE:

Adjustable fences can be positioned for varying thicknesses of stock

Guide

TOP VIEW

- Workpiece Fixed

Adjustable fence

NOTE:

Recess in center slot for fender washer

FIRST:

Center jig on workpiece

Guide

Va" plastic strip knob carriage bolt

Router platform

Adjustable

NOTE:

Distance between router guides equals width of router base

Washer

Fixed stop

Guide strip

VSxVA" machine screw

Adjustable fence

NOTE:

Adjustable fences can be positioned for varying thicknesses of stock

Guide

Adjustable fence

NOTE:

Recess in center slot for fender washer

TOP VIEW

- Workpiece Fixed

FIRST:

Center jig on workpiece

SECOND: Move adjustable stop to set mortise length

FEATURE YOUR JIG

If you've built an original jig and would like to see it featured on this page, send your idea to Woodsmith, Reader's Jig, 2200 Grand Ave., Des Moines, IA 50312.

If we publish it, we will send you $100 and a full set of Woodsmith back issues, with binders. Include a sketch (or photo), explain how if s used, and include a daytime phone number.

NOTE: Position router base against fixed stop for start of mortise

Fixed

Adjustable

NOTE:

Layout lines mark length of mortise

Workpiece

NOTE: Position router base against fixed stop for start of mortise

Fixed

Adjustable washer slides in

NOTE:

Layout lines mark length of mortise

Workpiece

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Responses

  • danny
    How to build a wooden segmented arch.?
    5 months ago

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