Alu-Pro Canvas Stretcher Bars and Crossbars: A Tutorial

Jackson’s Alu-Pro Ready-Made Canvases are extremely convenient. They come sized, primed, and mounted on a lightweight Aluminium frame for stability. But at Jackson’s we also sell a wide variety of Alu Pro Stretcher Bars, Crossbars and Accessories, for those artists who wish to stretch and prepare their own canvases to suit their particular needs.

This article aims to demystify the assembly process for Alu-Pro Aluminium frames and crossbars. First I will demonstrate the assembly of a frame to stretch and support a small or medium-size canvas; then I’ll take you through the assembly of a frame with a crossbar (used to brace large frames to give them extra strength). After that, I’ll show you how to attach hangers and use Spanners (the Alu-Pro equivalent of a Canvas Key, for tightening the canvas by extending the frame slightly at the corners). Throughout, I will let you know which of the Alu-Pro accessories are necessary for each process.

Assembling a simple Alu-Pro frame.

First, let’s go through the process of building a simple rectangular frame with no crossbar, which should be sufficiently strong for most purposes. I’ve chosen to make a frame of 40 x 60cm, using the shallow profile stretcher bars. (A deeper frame offers more space to affix the canvas, and will project the painting surface further from the wall.) This process will be essentially the same for any simple, unbraced frame which is square or rectangular; you can simply substitute different stretcher bar profiles and lengths.

For this frame, you will need:

– A 4mm Allen key, preferably an Alu-Pro Allen Key.
– A pair of Jackson’s Alu-Pro 40cm Aluminium Stretcher Bars. These are sold as a pair. As this is a small to medium-size canvas, I’ve chosen the slim profile Stretcher Bars which are around an inch thick, but if you would like a deeper frame with more space to fix your canvas, we also sell a version with a deeper profile. The profiles are not interchangeable; all four sides of your frame must be either deep or slim-profile.
– A pair of Jackson’s Alu-Pro 60cm Aluminium Stretcher Bars. These are also sold as a pair; remember to match the profile of the shorter sides! You can find the deeper profile bars of this length here.
– Four Alu-Pro Corner Connectors. Please note, these are sold individually.

Step 1.) Alu-Pro Stretcher Bars are made of spruce and aluminium. The wooden outer frame presents a smooth surface to the canvas, and can accept staples, pins and nails. The aluminium frame is used to bolt the whole apparatus together and maintain its rigidity even as the canvas tightens and relaxes in changing moisture conditions. These two sections might (or might not) slide over each other in transit. This shouldn’t cause much of a problem; simply slide the two sections until the ends are flush, as they are in this photo:

Step 2.) Take a 40cm Stretcher Bar, a Corner Connector, and a 60cm Stretcher Bar. Lodge one end of the Corner Connector into the inner slot on the metal section of one of the Stretcher Bars. I’ve added arrows to this cross-section diagram to show you where the Corner Connector is meant to sit – as you can see, the aluminium frame is the same on the slim and deep profile stretcher bars, so the process is the same.

Step 3.) Push the corner connector in as far as it will go, so that it looks something like the corner connector in the photo below. (For now, please ignore the flat, right-angled piece of metal which is sitting between the two Stretcher Bars in this photo. This is a Frame Stabiliser, and is only needed for very large canvases.)

Step 4.) Slide the protruding end of the Corner Connector into place on the other Stretcher Bar. Push the two bars together as tightly as possible and use the Allen key to tighten the nuts on the Corner Connector, fixing it to each Stretcher Bar in turn. It is possible to do this on your own, but it’s much easier if you have someone to help you. Get your friend to hold the bars together while you tighten the Corner Connector. You are aiming for a flush connection like this:

Step 5.) One you have secured two of the bars together, you should be able to slide all of the other Corner Connectors into the other Stretcher Bars to make a loose four-sided frame. Repeat the tightening process on all of the corners (you may need to tighten the first corner again). That’s the frame made: you’re ready to start stretching your canvas.

Assembling a frame with a Primary Crossbar.

Crossbars provide extra strength to Alu-Pro frames, as well as providing something of a handle by which the canvas can be carried. Further down this post you can find a table detailing when you will need a Primary Crossbar, when you will need a Secondary Crossbar, and what you will need to purchase to assemble them. For now, let’s just note that your canvas would need to be over 1.2 metres long on its longest side for you to ‘need’ a Primary Crossbar for structural reasons.

For this frame, which features a single ‘Primary’ Crossbar, you will need:

– A 4mm Allen key, preferably an Alu-Pro Allen Key.
– Four Jackson’s Alu-Pro Aluminium Stretcher Bars of whatever size you like. We will use 40cm and 60cm in this tutorial, simply because I’ve already got them to hand, though in reality you would never need to brace a frame this small with a crossbar (though you might add one for carrying convenience).
– Four Alu-Pro Corner Connectors. Remember, these are sold individually.
– Two Alu-Pro Support Connectors. These are used to fasten the Crossbar to the Stretcher Bars. They look like this:

– One Alu-Pro Crossbar. These come in a number of sizes, from 40cm, 50cm, 60cm and so on, all the way up to 200cm. Please do remember that a 40cm Crossbar is not actually 40cm long; it is designed to be used in parallel with two 40cm Stretcher Bars, and is only as long as the inside face of these 40cm Stretcher bars. It is, in fact, 27cm long, but you don’t actually need to know that. If you are using just the one ‘Primary’ Crossbar, you will want to be bracing between the two longer sides of your frame, so just make sure that you purchase a Crossbar which is (nominally) the same length as the two shorter sides of your frame. For this demonstration, we are using two 40cm Stretcher Bars and two 60cm Stretcher Bars, so we are using a 40cm Crossbar. The following photo will help you visualise this:

Step 1.) Lie one of the longer Stretcher Bars on the floor or on a table, metal side up.

Step 2.) Slide one of the Support Connectors into one end of the Primary Crossbar. You will be left with a piece of metal shaped like an Uppercase ‘L’ (with the Crossbar forming the ascender). Fasten the nut on each Support Connector.

Step 3.) The Support Connector will have a nut-and-bolt fastening mechanism dangling off it. Unscrew the nut as far as possible without detaching it from its screw, then place the Crossbar against the long stretcher bar which is lying on the floor, so that the nut hangs below the lip of the metal groove. The nut needs to sit below this lip in order to clasp the Crossbar to the Stretcher Bar.

Step 4.) Slide the Crossbar to the desired position and fasten it place using the Allen key. These photos demonstrate how the nut-and-bolt mechanism fastens to the metal groove of the Stretcher Bar:

Step 5.) Repeat this process at the other end of the Crossbar, attaching it to the other long Stretcher Bar using the other Support Connector. You’ll need to attach the other Support connector to the opposite side of the Crossbar so it’s on a diagonal from the one you’ve screwed in.

Step 6.) Bolt the rest of the frame together using Corner Connectors and Stretcher Bars, as demonstrated in the first tutorial. Tighten the Corner Connectors, and you’re done!

Note: If your canvas is large enough to require Secondary Crossbars (they would be at right angles to the Primary Crossbar and attach centrally to the Primary Crossbar’s sides and the middle of the internal side of each sidebar), use the same process to install them as you did with the Primary Crossbar. The only difference is, as well as attaching the bars with one support connector each, you will also need to attach one Cross Connector per bar, this makes a total of two support connectors and two cross connectors per full Secondary Crossbars installation. If you require more cross bars due to the size of your canvas, please check the table below to find out what materials you need.

Buying Guide to Alu-Pro Accessories.

In this section, I’ll take you through some of the other accessories which are used to assemble and hang Alu-Pro frames. Please note, all of the accessories (spanners, both types of hangars, Allen keys, crossbars, stabilisers) can be used with either slim or deep profile frames.

Before we begin to look at the accessories, this table might be a help. It shows how many of each piece you will need to order when building the different frames. In practice, you can use use two, three or four Support Connectors for a frame with a Primary Crossbar; the more you use, the stronger (and heavier) the frame will be.

I feel I should also note that while the table looks rather intimidating at first glance, it shouldn’t be; most artists would never work large enough to need to refer to the lower layers of this table, and I’d imagine that anyone building a 4.8 x 3.6m frame with three vertical and three horizontal crossbars will probably have a team of studio assistants to help them.

The various Alu-Pro accessories available on the Jackson’s website are as follows:

– Frame Stabilisers are used to reinforce the corners of large frames. You probably won’t need them unless you are stretching canvas over 200 x 200cm. They simply slot into the end of each Support Bar before a corner connector. These photos show where they should sit, and how to connect the two Support bars together:

– A 4mm Allen key is the only practical tool you will need to assemble any of the frames in this tutorial.

– Alu-Pro Screw Eyelets are used to hang your canvas. They can be placed at any point on the vertical sides of the frame, and are attached by a nut-and-bolt mechanism to the aluminium inner frame of the Stretcher Bars. The tightening process is the same as that for the nut and bolt mechanism on the Support Connectors: unscrew the nut as far as possible without detaching it from the thread of its screw, then place the Eyelet against the aluminium rim at the desired height. The nut should hang below the lip of the metal groove. Then just twist the Screw Eyelet to tighten it in place. Please remember to buy two!

– If your painting is too large to trust to the Screw Eyelets, you can use Alu-Pro Heavy Duty Hangers instead. Again, you will need to purchase two. Because of their shape, they are slightly simpler to attach than the Eyelets; place the Heavy Duty Hanger against the aluminium frame so that the two nuts sit deep in the groove. (You may need to loosen the nuts for them to protrude below the rim.) Then tighten with an Allen key.

– Alu-Pro Extenders can be used to connect two stretcher bars. This will allow you to stretch and support very, very large canvases. They look like a section of a Stretcher Bar, but have two connecting strips’ – small lengths of metal which sit inside the groove on the inner side of the aluminium frame. These are used to secure the Extender to the Stretcher Bars on either side. Simply slide the extender between the two stretcher bars you wish to connect, then put the connecting strip over the join and tighten with an Allen key, making sure two nuts lie on either side of the connection. This process is easier to depict than describe, so we’ve created a short photo-demonstration:

– Alu-Pro Spanners are slightly confusingly named, since they don’t look like a normal spanner, and you will actually need an Allen key to use them. They are the Alu-Pro equivalent of a Canvas Key; that is, they are used once the canvas has been attached to the frame and stretched, to tighten the canvas by extending the frame slightly at the corners. They are fastened with a nut and bolt mechanism. First you must attach the spanner to the frame, just outside the Corner Connector, like this:

Then use the Allen key to release the nut closest to the Spanner on the Corner Connector.

Now use the Allen key to thread the screw through the aperture on the Spanner, so that it places pressure on the Corner Connector and pushes the frame apart slightly at the corner, tightening the canvas.

Once you’ve extended the frame, tighten the nut on the Corner Connector again, and repeat this whole process on as many corners as necessary until the canvas is taut. All done!

Browse and shop our full range of Alu-Pro Stretcher Bars, Crossbars and Accessories, or visit our tutorial for using wooden stretcher bars.