Backing plate confusion

C

charlieo

New member
Hi all, I have a PC 7424XP from 2009. The velcro separated from the foam of the backing plate so I need a new backing plate.
The box refers to a 6" counterbalance, but after I remove the backing plate from what I believe is the counterbalance, it reads `use 5" pad only`.

My backing plate measures ~4 3/4", and I use 5.5" pads.
Am I correct in thinking that I need a 5" dual-action backing plate with the appropriate spindle?
And I`m ok using 5.5" pads apparently?

Can someone confirm that these are 2 valid choices? If so, being a 3M fan, I`ll probably go for that.
Thanks for your help.

3M Hook-It 5 Inch Dual Action Backing Plate - 5775
Dual Action Flexible 5 inch Backing Plate
 
charlieo said:
Hi all, I have a PC 7424XP from 2009. The velcro separated from the foam of the backing plate so I need a new backing plate.
The box refers to a 6" counterbalance, but after I remove the backing plate from what I believe is the counterbalance, it reads `use 5" pad only`.

My backing plate measures ~4 3/4", and I use 5.5" pads.
Am I correct in thinking that I need a 5" dual-action backing plate with the appropriate spindle?
And I`m ok using 5.5" pads apparently?

Can someone confirm that these are 2 valid choices? If so, being a 3M fan, I`ll probably go for that.
Thanks for your help.

3M Hook-It 5 Inch Dual Action Backing Plate - 5775
Dual Action Flexible 5 inch Backing Plate
Click to expand...

charlieo -
Any 5 inch or so, backing plate for the Porter Cable will work just fine with any 5" - 5.5" pads..

I would never use this small of a backing plate (5") with 6" pads..You want the backing plate to support All of the foam pad..

Here is the one I saw at the Autopia Store --- Dual Action Flexible 5 inch Backing Plate

Dan F
 
Thanks Dan, it looks like they`re ok going up to 5.5" pads on these, since this was all purchased at the same time from Autopia.
I`ll confirm with them tom`w.
 
charlieo said:
Thanks Dan, it looks like they`re ok going up to 5.5" pads on these, since this was all purchased at the same time from Autopia.
I`ll confirm with them tom`w.
Click to expand...

charlieo - Yes, either of those backing plates you linked will work great with all foam pads in the 5" - 5.5" diameter... Been using these combos on my Rotary for decades...
Dan F
 
Don`t pay attention to the counter weight on your PC. Different CW was meant for sanding, it will not affect your polishing.
 
charlieo said:
Thanks all, I went with the Lake country, fwiw.
Click to expand...

Hey, charlieo !
I have had great results from Lake Country Backing Plates in all sizes, for over 15 years...
They have all been great, no issues, perfectly round, and never had an issue with them..

The only other ones I ever tried were some 3M from England that were both out of round and useless..
Good luck with your project !
Dan F
 
Well, let`s put this "which counterweight should I be using on the Porter-cable 7424 with what size backing plate" controversy/issue to rest.
Here`s the link to a thread discussion on this very issue. You will need to go to Post #9 by (former) Autopian Eliot Ness for his critical assessment. Yes, it`s an old thread from June, 2008, but the PC-DA 7424 has been used for vehicle polishing and correcting long before that.
https://www.autopia.org/forums/car-...g-counterweight.html?highlight=counter+weight
(Sorry, no spoiler alert. You make your own judgement after reading the thread info there.)

By the way, Porter-Cable did do one thing right in using two round-head screws with a combination slotted-&-Torx socket drive for mounting the counterbalance. The Torx drive socket size is a T20. Use the correct Torx drive bit to loosen or tighten the two mounting screws if you are changing out the counterbalance OR just tightening the mounting screws for the counterbalance that came as Original Equipment of Manufacturer (OEM) with the PC-DA 7424, which does state for 5" pads only. DON"T use a flat-tipped (blade) screw driver with the slotted drive. I think we all know how many screws, especially countersunk flat-heads, that have been damaged beyond removal because the single slot was stripped out or rounded over from over-zealous tightening with a flat-tipped screwdriver!
 
Lonnie said:
Well, let`s put this "which counterweight should I be using on the Porter-cable 7424 with what size backing plate" controversy/issue to rest.
Here`s the link to a thread discussion on this very issue. You will need to go to Post #9 by (former) Autopian Eliot Ness for his critical assessment. Yes, it`s an old thread from June, 2008, but the PC-DA 7424 has been used for vehicle polishing and correcting long before that.
https://www.autopia.org/forums/car-...g-counterweight.html?highlight=counter+weight
(Sorry, no spoiler alert. You make your own judgement after reading the thread info there.)
Click to expand...

I can *almost* remember that thread :D

Guess I won`t play spoiler (by posting my experience/opinion) either....but we`ll see how things turn out for charlieo
 
The issue that I had was that the box read `Includes 6" proprietary counter balance for use with 6" sanding/polishing pad`, but the PC itself had the smaller counter balance. I`m guessing that there was a period when Autopia Car Care was getting these modified (or modifying themselves) with the smaller counter balance but it was not reflected on the box.

When I spun the new Lake Country backing plate, looking from the side: while the steel studs appear to be true, the pad seemed a bit uneven, appearing to move a bit up and down as it rotated: I`m assuming this will work itself out, or in light of the fact that I`m sometimes using a bonnet (which is hardly purely balanced), this is not a concern, we`re not dealing with perfection here.

(Update: it appears that the bolts are also not moving in a level plane as the plate rotates, so unless this is to be expected to a degree, I think I got a bad backing plate.)
 
charlieo said:
The issue that I had was that the box read `Includes 6" proprietary counter balance for use with 6" sanding/polishing pad`, but the PC itself had the smaller counter balance. I`m guessing that there was a period when Autopia Car Care was getting these modified (or modifying themselves) with the smaller counter balance but it was not reflected on the box. When I spun the new Lake Country backing plate, looking from the side: while the steel studs appear to be true, the pad seemed a bit uneven, appearing to move a bit up and down as it rotated: I`m assuming this will work itself out, or in light of the fact that I`m sometimes using a bonnet (which is hardly purely balanced), this is not a concern, we`re not dealing with perfection here.

(Update: it appears that the bolts are also not moving in a level plane as the plate rotates, so unless this is to be expected to a degree, I think I got a bad backing plate.)
Click to expand...

Remember, the reason for the counterweights is for the original reason this machine was made = for sanding.. Have you even used your machine yet?

I have a brand new one that I only occasionally use for cleaning glass surfaces because the machine is tiny compared to my Rotary and it is very easy to use one handed..

I went out and looked at it and spun the used 3 inch backing plate and it appeared to not have a perfectly "true" rotation either..
So, I took the used one off and put on a brand new 3 inch backing plate, spun it and it appeared to more "true" when I spun it.

Then, I looked at the 2 spacers on the backing plate screw in shaft, and one is like a hard rubber and the other is a thinner fiber spacer..
These spacers are there so that the backing plate does not go all the way down and hit the counterweight.

Sometimes, these spacers get a little off, and that alone might make the backing plate not rotate perfectly "true" to the eye..
I removed and repositioned both spacers on the backing plate screw in shaft, installed it, and it rotated more "true" that it had before..

Something else to consider - this Porter Cable is still a random orbital machine, it will never be rotating fast enough in use, to make a difference in how "true" it rotates..

I really doubt that Lake Country is going to make badly out of round backing plates, based on my use of them for well over a decade and never had a problem one..
Dan F
 
SO, here`s a question on backing plates then:
Are backing plates designed to be used on rotary buffers made to "better specifications" for roundness or trueness (sometimes referred to Total Indicator Runout, or TIR as measured with a runout inspection gauge) and better balanced because of the type of motion that they go through and the rotational speed (AKA, RPMs) that they may be used at on a rotary than those designed for Dual Action- Random Orbitals??

Here`s another related question concerning the Griot`s Garage redesigned BOSS G21 and G15 buffers.
They have an ingenious Weight Optimization System designed for use with foam pads of various thickness and, hence weight, that utilize different color-coded screws of different weights to help act as counterbalances to minimize the vibrations when operating these machines with those types of pads.
They have developed them for use with both the 6" backing plate and the 5" backing plate and their pad types for use with their buffers. From GG`s Operating Manual they are:
1) Silver for their Microfiber pads
2) Black for their 1" thick pads
3) Copper for their 5/8" thick pads
So, for those Autopians who have these GG BOSS buffers or different size backing plates, how well do these counterbalancing screws work OR do you even change them out for the type of pad you are using??
 
My personal favorite for a PC is the Meguiars Soft Buff DBP5 DA Polisher 5 inch Backing Plate
It`s made solid, "Molded one-piece construction provides durable performance, detail after detail."
...and it has white lines on the backing plate to ensure that you can visibly see the pad rotation.

I personally only use 5" pads. With a PC (and all DA`s) the 5" size allows much better control.
I even use a 5" backing plate on my RUPES BigFoot LHR21 MARK III Random Orbital
As a matter of fact, I can not even remember the last time I used a 6" pad.
 
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