A DIY Shop Tool for Making Torque Plates

Long story short: I needed torque plates for an aluminum frame build. I wanted open plates instead of the kind with axle through-hole. I've made dropout plates before and although it's not difficult, with just hand tools for sawing and filing it's fussy time consuming work. With another build planned with similar requirements, it seemed worth the effort to make a tool to simplify torque plate fabrication.

The Idea

The angle grinder is a mainstay of metal fabrication but it's a 'big arm muscle' tool that limits fine control when moving the grinder into the work. The idea is to jig up a mount and table so small hand muscles can instead move the work into the fixed grinder so closer tolerances and finer finish are possible.

The Result

This torque plate is cut from 1/4 inch 304 stainless and was made with the tool described below -- without hand sawing or filing (well - save for light filing to remove grinding flash from the lower edges).


The Tool

The tool consists of a mount to firmly hold a 4 1/2 inch angle grinder (Makita with Paddle switch) and a table to position the work. The table can be adjusted so the center line of the work is on a radius of the cutting/grinding wheel to give a square bottom to the kerf. It can also be dropped so work up to 3/8" can be ground without running into the grinder disk retaining nut. The thing cuts and grinds really fast and gives a nicely finished perpendicular edge. A shop vac pickup keeps the air more or less free of smoke and cutting waste.


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• The fore and aft grinder mounts are scrap wood with a pair of rubber feet (Home Depot) screwed down. The circular body of the grinder rests on/between the feet so no fancy shaping of the mount is required - all simple square cuts. These two ends are joined by a base piece to form a pedestal that can be mounted to anything. There are two 3/8" holes in the pedestal base piece which is held down to the base with 1/4" bolts and fender washers so the pedestal can be slid around a bit to get it square with the table. The base is chopped from a scrap particle board shelf from the dump. All components are bolted to the base using M5 sheet metal rivnuts set into through holes or using EZ-Lok 1/4-20 threaded inserts. This allows easy and repeated assembly/disassembly in spite of the particle board.
  
  
• Two stainless 4 1/2" spring loaded turbo intercooler T-bolt clamps (search: eBay) were cut into two sections, drilled, and screwed down to form the retaining straps. The spring-loading feature is nice, but not strictly necessary. The provided clamping nuts were nice and tall but had a tight friction fit. As an alternative to replacing them for ease of use, a tap was run through to get standard clearance. Adjustment is easy with a deep socket and ratcheting Harbor Freight finger-grip handle .
  
  
• The table is cut from a bit of 1/8" 5051 aluminum leftover and screwed to some particle board legs. The sliding mounts were made by slotting some aluminum channel. In the low position the table allows clearance for 3/8" material to pass under the grinder retaining nut and can be raised to whatever height is appropriate for the thickness of the work to get a square-bottom kerf. A couple of particle board spacers were run off to make it easy to set the raised height for 1/4 inch plate. An alternative to an adjustable table would be to simply knock up a couple of separate wooden tables or legs and use whichever was appropriate.
  
  As it turns out the aluminum gets dug up by the grinding flash on the lower edge of the work so it's necessary to stop from time to time to strip the flash off the bottom corner with a few file strokes. A few quick rubs with a sanding block smooths the aluminum plate when the job is done. That said, a wooden table top with a scrap of duct work sheet metal tacked on the deck might avoid some of this.
  
  
• The vacuum pickup was not planned, but a lucky find of a discarded curved shop vac extension at the dump supplied the part. A little reshaping with a hot air gun squeezed it a bit. Two hose clamps drilled and screwed to the base hold it in place. Without this, a bit of aluminum flashing (Home Depot) was going to be tacked to the base to deflect the molten grinding particles.
  
  
• The 3/16" polycarbonate shield (search: eBay) is simply screwed into the handle mount of the grinder. The mount was made from bits of aluminum angle but there are many mounting alternatives (I was going to use the gooseneck from an old desk lamp before the present mount idea popped up). In spite of the fixed shield, a full face shield is recommended...
  
  
• I already have a 6 inch disk table sander (part of a belt sander), but lacking that, this jig could do sanding as well. It's hard to find rigid sanding disks for these angle grinders so I would probably just use a common 6" stick-on sanding disk stuck to a thick 6" cutoff wheel (cut out the arbor hole in the sanding disk). This would give a pretty stiff fiberglass reinforced disk that should give a good finish for long straight work edges.

Anyhow - the idea is pretty simple and there are many ways to do this using stuff that's on hand.


Making a Torque Plate

Because a small error or variation in the slot can throw off the holes and edges quite a bit, the idea it to cut the slot first, then lay out the rest of the part to accommodate however the slot comes out. This allows fairly imprecise slot alignment during fabrication but with a nicely aligned final product.

My first plate is shown above. Here's some shots of making the second plate for the drive side of the frame.

• Layout was done from paper cutout to get rough location and orientation of slot. The work was cut oversize to allow adjustment for angle errors, etc. The table assembly imposes limits because of limited 'throat' - the space between cutting wheel and gear head. Because of this, cutting the work piece from the stock plate and certain rough cuts were done freehand with the unmounted grinder. These rough cuts are discarded later anyway, so precision and skill are not an issue. Smaller rough cuts were done last using the table to trim the work just enough so that it could lie flat on the bike dropout for fitting/marking.
  
  
• The slot was cut by drilling a roughly 8mm hole then making two parallel cuts to free the center chunk from the slot. A 'no-drill' alternative would be to make the two side cuts then two diagonal cuts leaving a pointy bottom to the slot to be ground flat. The slot was made about 2mm too narrow and not quite deep enough; a fresh grinding wheel with nice square edge was used to bring the width to spec and grind to depth. Unlike the thin 0.045" cutoff disk, the grinding wheel is 0.25" thick and the wheel edge easily makes a smooth square bottom to the slot. A spare axle was used to continually check the fit ($12 MAC replacement axle from EM3EV - a handy 'tool' for dropout and TA work). So - no hand filing at all to make the slot.
  
  
• With the slot cut, the part was mounted up and clocked fully in the direction of wheel rotation. The holes were then marked and drilled. Since motor torque tries to spin the shaft counter to wheel rotation, this ensures the torque plates - not the frame - will carry the rotational load. This was for a geared hub with uni-directional torque - centering the slot with the test axle would be recommended for a DD with regen.
  
  Due to a drilling whoops I needed to file one of the holes slightly so the loaded position of the plate properly shared torque with the other plate. A chainsaw file is a good choice - long and round with a constant diameter the entire length.
  
  
• After the part was clocked to the proper position and the holes drilled, the exact orientation on the frame became finalized, so the excess material was marked then cut and ground away to get a nice visual appearance. Cutting goes so quickly that there is no real penalty to this double 'initial rough cut/final finish cut' strategy. After grinding, the edges were sanded using a table disk sander to get a finer finish - but this wasn't strictly necessary. The faces were hand sanded a bit with 60 grit then 100 grit emery cloth - again not really necessary.

Anyhow - these first torque plates came out pretty spiffy and I'm pleased not to rely on generic TAs or iterations with Big Blue Saw. The slotting, cuts, and shaping went quickly and it was nice to skip the sawing and filing stuff...

• FWIW: I was going to make these first plates out of common mild steel bar stock (Home Depot, eBay, etc) but went with the 304 stainless on a lark. There was no real downside to cutting and grinding the stainless, but tapping was very difficult and time-consuming (not much fun to drill either). I would really recommend mild steel if tapping is part of the design.

Fabricating this gadget probably isn't for everyone, but if you have an angle grinder in hand, some scrap bits and pieces around the shop, and see some builds in your future, it might be worth tacking together something similar....

Nice! I like it alot!
You may be able to make up the jigs and sell them.

Brilliant!...I like it a lot. More parts can be made by ordering water-jetted or laser-cut, but ordering single pieces during the prototype stage is quite expensive. There are price breaks per part if you order ten of a design, but it is tedious to make several revised modifications and then wait for delivery each time.

If I get a great new idea, I can buy materials locally, and then create/test-fit/V2/V3/etc...all in one weekend.

Torque-plate selection is one of the areas that is sorely lacking in the hubmotor world, and will likely remain that way as long as new frame designs keep coming out...

Lovely.
Whilst the ISO mounts are always in the same position relative to the axle center, the axle's angle of rotation about the centers varies.
This drives me nuts.

The ampedbikes solution of the little star insert never sat well with me for mid to high power - too much slack.
I like this a lot. Well done.

Or, flying closer to the sun, clamp your grinder into some kind of vise. But that does make a big risk for jamming up the workpiece, and sucking a hand in.

FWIW, your jig resembles the smaller tile saws a lot. Just saying, if you plan on tiling your house too, BINGO.

OR, if you have a table saw, chuck a metal cutting blade into that.

I've been making quite a few torque arms lately, to fit the rear of various bikes. I'm creating a stockpile of TA's that will easily fit whatever bike I'm fooling with at the moment. So I don't have to stop progress to make a new TA each time. Some of the TA's fit to the disk brake mount, but you cut a custom hole to bolt up, others fit the derailleur side.

I've been just making rough cuts on my metal cutting chop saw, then roughing out the shape on a regular grinding wheel. The grinder is slower, but fine for the outside shaping.

I planned to buy an angle grinder support but now that I see how you did your, I might prefer your option

To sort of clarify, I looked to address two problems with the jig:

1. cut and fully finish a precise slot with no sawing or filing at all
2. perform the grosser edge shaping with clean perpendicular cuts

The second is relatively easy and comes pretty much for free if the first can be accomplished, but the reverse is not necessarily true.

The illustration below shows my thinking on the issue of table height. A disk spindle lower than the table surface (as with common saws) is fine to accomplish (2) but leaves (1) a matter of guesswork because the undercutting does not match the layout marks on the work - and the cut requires additional finishing to bring it perpendicular.


The ability to finish the slot by machine means working the width to a snug fit and the depth to a square bottom. This led me to grinding with the same center line requirements as (1) but with a table slot that would accommodate a grinding wheel.

As always, there are many options to make do with the tools at hand - every fabricator does this. However, there are always tools like this one - a 'one trick pony' that really isn't good for much else but does that one trick pretty well...

Anyhow - hope this gets you thinking about ways tackle torque plate fabrication - no matter how you accomplish it.

Nice jig! I use a band-saw or hand held jig-saw. Creates less heat, so you don't lose the temper of the steel and cuts corners straight...... But that's a great idea, sorta like a mini table saw!

You don't think it's a big deal having the torque arm groove flat at the top rather than rounded?

You also might consider cutting off the tails at the bottom of the groove at 45 degrees to allow for sort of automatic guiding for the axle entry into the dropouts.

bowlofsalad said:

You don't think it's a big deal having a it flat at the top of the groove rather than rounded?

Click to expand...

The torque plate and its fasteners are not intended to carry the weight of the vehicle; the axle supports the frame by the frame dropout - not by the torque plate.
The sides of the torque plate slot prevent axle rotation - the bottom of the plate slot need not even touch the axle -- no downside to a flat bottom.

bowlofsalad said:

You also might consider cutting off the tails at the bottom of the groove at 45 degrees to allow for sort of automatic guiding for the axle entry into the dropouts.

Click to expand...

On this bike the derailleur hanger is aligned with the dropout and provides a ready-made guide to rotate the axle flat into position for a smooth entry. Slides in slick every time.

Excellent idea and neatly executed.
Quality end products & photos also !
Agree with BoSalad that a pre drilled radius end to the slot might be a sensible mod and make the finishing simpler.
The "flat bottom" of the slot and sharp corners lead to high stress concentration points should the axle torque actually load onto the Torque Arm.

Hillhater said:

Agree with BoSalad that a pre drilled radius end to the slot might be a sensible mod and make the finishing simpler.
The "flat bottom" of the slot and sharp corners lead to high stress concentration points should the axle torque actually load onto the Torque Arm.

Click to expand...

As far as ease of construction - accurately positioning and drilling a 10mm hole in 304 stainless is not easy. To accurately match the curvature of the axle, the end cannot be simply drilled to 10mm, it must be worked to a 14mm radius. By comparison, the grinder makes a finished bottom cut almost without effort - flat or otherwise.

Rounded corners are certainly desirable in the aluminum frame dropout when it is filed deeper - precisely because of stress risers. However, the thickness and material of the torque plates can easily be selected to make corner stress a non- issue. In this case a total of 1/2 inch of 304 stainless plate for a 2kw motor makes discussion of stress fractures completely academic.

That said, if radiused slot corners are desired, it's only necessary to use a grinding wheel with rounded corners on the disc edge (used not new).

In any case, thanks for the kind words - I'm glad you enjoyed the post...

That is a way cool tool with lots of thought behind it. I prefer a bandsaw for cutting steel, but stainless is a different story and destroys bandsaw blades. Ask me how I know this. I would make my torque arms out of 3/8" mild steel. Definitely not as pretty as yours but a bit of paint and, done. It is still an amazing design.
otherDoc

Nice work and nice writeup. This would be the perfect tool to sit next to the bench grinder. I still have a sore neck from grinding a drop out over the weekend!

Nice.

That is a good idea, the way your saw is positioned relative to the blade. I've just used saws so many decades, I make the adjustment for it without thought at all. Flip the piece, cut again from the other side.

Definitely no need for a curved bottom of the cut. It's support on the sides you are after. Very nice work!

Very sweet little tool holder! I've certainly cut my fair share of torque plates by hand, and this would be far easier. Now I have a band saw, but it doesn't offer the ability to get square corners unless the slot is wider than the blade depth.



A similar option is to adapt a regular grinder to hold angle grinder blades. Not as easy though, as it requires either luck of finding the right combination of parts or an ability to make the adapter from scratch. I tried a few years back and didn't have the means or the right luck. Might do this instead!

or maybe just get a stand:
http://www.amazon.co.uk/Wolfcraft-5019000-Angle-Grinder-Stand/dp/B000P3DX6K/ref=sr_1_1?ie=UTF8&qid=1451127620&sr=8-1&keywords=angle+grinder+bench

This is an excellent idea, really transforms a tool with relative hack reputation to something that can be used to make something more accurate and professional. Further, available and affordable for the common man. Brilliant! 8)