Gents, I always have a lot of trouble cutting the 15.9 by 14mm hole for fitting Cord Grip Grommets when upgrading the power cord to Australian standards on my old radios.

Does anyone know of the availability of a chassis punch to cut the hole?

Gary,
Easier to use a gland and install it backwards.
I struggle with those clamps, been looking for a proper tool for ages
Ben

Only a nibbling tool and a file would do the trick for most people. Those with toolmaking skills could make themselves a punch set but for a few holes the most authentic way to protect flexible cords is with a traditional grommet. With this you would install a cable clamp under the chassis in place of the knot that manufacturers used to tie in the cords. Both items are available at Jaycar.

Yes, make it easy on yourself and go for round holes. I use a step drill.

Aldi occasionally has step drills on offer.

Trick is to make a round hole so that the clamp grommet is a tight fit and, after installing the cord, glue the rear of the grommet into place with contact adhesive so it can't rotate in the chassis.

I just use a standard grommet and I wrap a load of electrical tape around the cord just inside the grommet, so that it can't pull through, I then araldite the face of the grommet and pull the cord tightly so that the electrical tape around the cord pulls flush with the araldited grommet.

The things relevant & often overlooked:

Electrical tape is not permanent the adhesive commonly fails & the cable slips.

If the cable can rotate there is the danger of it fatigue failing the live wires and I have seen a few do that.

With cables with the rubber cable sleeve that the nut tightens too a bit of decent super glue like Loctite 401 between sleeve & cable stops any twisting. A zip tie with a long tail will also stop pulling (also glue) and reduce twisting in the unlikely event the nut comes loose.

Leaving the seal that goes on the body, off. Reduces the risk of the nut coming undone, even when glued as well.

Leave the earth tail long, so that if it does suffer enough tension to break the grommet it's last to fail.

Impact punching is never a good idea with the valves in place.

A burr can be used to cut the hole oblong. They are not cheap: I often use one in the (lathes) tool post grinder (off lathe), in a ways they were not exactly designed for.

I do have step drills, magic in thin metal.

Agree a punch for those mains grip grommets would be a handy thing.

Every time I do one with drill and file its a slow tedious messy job and never seem to get it right.

I have punches for valve sockets these are a die with a bolt to pull the die through: I have used , it successfully on 16 Gauge, which is why it no longer has the original bolt. Stresses the hell out of it.

The biggest hassle with a die is the size and the need for the cutter to be "case hardened" (tool steel). This is why, if I go that way, I use the Bottle Nosed Grinder (Straight Grinder). You can, as noted, by burrs in variety of shapes & sizes. Many of these are made to cut on there sides (like router bits). Ordinary jobber drills will too, but not well.

If you do a lot of these holes in constricted areas, that may be cost effective in the bigger size? Also note that even in a drill press starting a hole where the drill bit can squirm away, aside from a centre punch which might be impractical, a lathe centering drill will not squirm. So you start with it.

Nibblers are messy & often suffer the space issue. Make sure you protect anything that could get hit by the burr & swarf.

Found a punch in the USA. They are called Double "D" punches.

https://www.boltproducts.com/srp-625-550-p-4685.html

Fits the Altronics, H4270, 7.4-8.2mm Cord Grip Grommet.

Maximum steel thickness is 12 Gauge (2.78mm).

I have contacted them and asked for a price for 10.

Definitely an option, price will be the factor & if it is actually made in USA, its probably real (ASTMxxxx) metal fit, for purpose.

Greenlee makes a range of Double-D punches, but they are in the US$200+ price range, before shipping.

I think the 625-550 is made by Heyco:

https://www.heyco.com/Strain_Relief_Bushings/product.cfm?product=Relief-Mounting-Hole-Punches

Yes I think the one from Boltproducts will be the same price, unfortunately.

Punches like that have to be hard & strong due to the force. That works exactly the same as the one I have for doing socket holes etc.

The biggest handicap is finding a spot to get the whole assy in when there are parts in the road. It might have more hope if it was a "linear broach". I have used a file to elongate the hole for a double "D", a drill bit and a burr.

Burrs are not cheap either. But I do use them in the die grinder (tool post grinder (bottle nose type)), on the lathe, but the die grinder can be used off lathe.

Mine has a longer nose than this one & has a HM collar arrangement made for its nose for the tool post. Beware: You buy the right industrial grind stones for these and a full face shield.

https://www.boschtools.com/ca/en/boschtools-ocs/die-grinders-dg250c-36138-p/

Glands installed pointy end in are often better without the body washer (Can come undone): Not the one on the cable.