You have probably seen more and more timber frame designers and customers ask about adding steel plates to their projects.  This is a fine engineering solution to reinforce your frames, but the steel plate slots must be cut accurately or it defeats the purpose.  So it is important for you to consider the best slot mortising tools available before tackling these projects.

At Timberwolf Tools, we have two clear recommendations for cutting slots:  Mafell's LS 103Ec Slot Mortiser and Deep Slot Mortiser.  So if you have a traditional Mafell LS 103Ec chain mortiser in your shop, you're already halfway towards cutting the best slots.  Today we will compare these slot mortisers side-by-side to help you determine which option pays the most dividends for your business.

Mafell LS 103Ec Slot Mortiser

This setup with the Mafell SG 230 Slotting Guide can plunge 11-3/16" either vertically straight up and down, or horizontally into the end-grain.

Vertical Slot Mortiser Horizontal Slot Mortiser

The SG 230 version is great for cutting slots in solid wood, trusses, laminated beams and glulam.  Its key slotting applications include beam joints and connectors (exposed and concealed), post anchors, supporting legs, channels for supply lines, integrated transition pieces, and gusset plates.

With a low overall weight of just 37 pounds, a torsion-free guide support stand, and a comfortable handle:  the SG 230 is easy to use in challenging positions, even when mortising slots in fitted beams.

Several features work together to ensure perfectly executed slots.  The stand includes a powerful retraction spring allowing for either 8-5/8" or 11-3/16" plunges (220 or 285mm).  There are 16 different chain options with millimeter-precise widths ranging from ~1/4" to ~13/16" (6 to 21mm).  And the clamp is continuously adjustable with easy-to-read scales for series production purposes.

Timberwolf Tools has several of these excellent slot mortisers in stock.  With each LS 103Ec Slot Mortiser purchase, we will include a FREE grease gun and premium bearing grease that you can pump into the bottom of the bar, plus FREE chain lubricant for lasting performance.

For more information & video of this slot mortiser, please view:
Mafell LS 103Ec Slot Mortiser on
or in the Mafell Online Catalog

Mafell LS 103Ec Deep Slot Mortiser

This setup with the Mafell SG 400 Slotting Guide can plunge approximately 15-11/16" either at angles up to 45 degrees, or straight (typically used horizontally)

Mafell LS 103Ec Deep Slot Mortiser

The SG 400 version is ideal for cutting steel plate slots in large glulam workpieces, as well as slots for high quality gusset plates in engineered lumber.

Its impressive mortising depth and angles are made possible by the exact coordination of the slot attachment with your chain mortiser.  With a special chain guide, cutting depth stop, and vertical edge spacing scale, the Deep Slot Mortiser guarantees precision with each plunge.

You have two options for chain bars.  The longer 15-11/16" (400mm) bar gets you the most depth for straight and angled slots, and works with chains between 3/8" and 11/16" wide (10 - 17mm).  The shorter 11-13/16" (300mm) bar is compatible with chains between 1/4" and 11/16" wide (6 - 17mm), making it a good option for thin angled slots.

The SG 400 is best used with a 240 V LS 103Ec Chain Mortiser, which has advantages compared to 120 V motors when plunging very deep into wood.

For more information & videos of this slot mortiser, please view:
Mafell LS 103Ec Deep Slot Mortiser on
or in the Mafell Online Catalog

Mafell LS 103Ec Slot Mortiser Mafell LS 103Ec Deep Slot Mortiser
Slot MortiserDeep Slot Mortiser
Mortising Depth 8-5/8" or 11-3/16"
220 or 285mm
11-13/16" or 15-11/16"
300 or 400mm
Mortising Width (1 cut) 1/4" to 13/16"
6 to 21mm
1/4" (or 3/8") to 11/16"
6 (or 10) to 17mm
Mortising Length (1 cut) 1-15/16"
Weight (with LS 103Ec) 37 lbs
16.7 kg
54 lbs
24.5 kg
Tilt Range N/A 45°

Metric measurements are exact, customary measurements are rounded

Slot Mortising FAQ

What size chain do I need for 1/4" steel plates?
It is technically possible to use a 7mm chain/bar/sprocket for a 1/4" plate, but in practice, 8mm is better since you need a little bit of space between the steel plate and the slot when assembling the plates in the wood.

What size chain do I need for 3/8" steel plates?
Similar to the example above:  it technically possible to use a 10mm chain/bar/sprocket for a 3/8" plate.  But in practice, 11mm is better since you need a little bit of space between the steel plate and the slot when assembling the plates in the wood.

How many chains should I order?
While you don't need to have two chains, it is quite valuable on a practical basis to have two, so that you can continue to make slots while one of them is being sharpened.

Do you have a slot mortiser that can go deeper than 15-11/16 inches?
There is also the Mafell SG 500 that plunges as far as 19-1/2" if your accountant says you need to spend $15k by year's end.  But the SG 230 or SG 400 version is usually a more practical option.

Can I just eye-line with a chain saw?
If you can pull that off, you probably don't need to be on our e-mail list :)


In a past email I hinted at some possible dirndl/lederhosen photos from Germany, and it's time to deliver:  Kate and I will be definitely be reminiscing about Munich's wunderbar water+barley+hops combos during the sub-zero temps in our not-too-distant future.

May your driveways be properly plowed and sanded this season!  You never know when FedEx might show up with some tools...


Jeff Powell and the Timberwolf Tools family
Toll free:  800-869-4169