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 Cutting the hole for fitting Cord Grip Grommets to old radios
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 Return to top of page · Post #: 1 · Written at 5:37:37 PM on 31 May 2017.
Garyoz's avatar
 Location: Perth, WA
 Member since 19 November 2008
 Member #: 381
 Postcount: 237

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?


 
 Return to top of page · Post #: 2 · Written at 6:35:38 PM on 31 May 2017.
Redxm's avatar
 Location: Tamworth, NSW
 Member since 6 April 2012
 Member #: 1126
 Postcount: 436

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


 
 Return to top of page · Post #: 3 · Written at 6:41:17 PM on 31 May 2017.
Brad's avatar
 Administrator
 Location: Greenwich, NSW
 Member since 15 November 2005
 Member #: 1
 Postcount: 5620

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.


‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
A valve a day keeps the transistor away...

 
 Return to top of page · Post #: 4 · Written at 7:16:49 PM on 31 May 2017.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 5340

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


 
 Return to top of page · Post #: 5 · Written at 8:36:43 AM on 1 June 2017.
STC830's Gravatar
 Location: NSW
 Member since 10 June 2010
 Member #: 681
 Postcount: 842

Aldi occasionally has step drills on offer.


 
 Return to top of page · Post #: 6 · Written at 10:01:29 AM on 1 June 2017.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 1345

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.


 
 Return to top of page · Post #: 7 · Written at 12:19:12 AM on 2 June 2017.
JamieLee's Gravatar
 Location: Clare, SA
 Member since 27 March 2016
 Member #: 1894
 Postcount: 505

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.


 
 Return to top of page · Post #: 8 · Written at 10:01:38 PM on 2 June 2017.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 3856

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.


 
 Return to top of page · Post #: 9 · Written at 7:37:01 AM on 11 June 2017.
Simplex's Gravatar
 Location: Bathurst, NSW
 Member since 7 August 2008
 Member #: 336
 Postcount: 297

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.


 
 Return to top of page · Post #: 10 · Written at 8:59:21 AM on 11 June 2017.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 3856

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.


 
 Return to top of page · Post #: 11 · Written at 10:37:03 AM on 19 August 2017.
Garyoz's avatar
 Location: Perth, WA
 Member since 19 November 2008
 Member #: 381
 Postcount: 237

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.


 
 Return to top of page · Post #: 12 · Written at 12:10:11 PM on 19 August 2017.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 3856

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


 
 Return to top of page · Post #: 13 · Written at 1:02:28 PM on 19 August 2017.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 5340

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


 
 Return to top of page · Post #: 14 · Written at 5:57:10 PM on 19 August 2017.
Garyoz's avatar
 Location: Perth, WA
 Member since 19 November 2008
 Member #: 381
 Postcount: 237

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


 
 Return to top of page · Post #: 15 · Written at 10:21:19 PM on 19 August 2017.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 3856

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.


 
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