Rupes 21 markII backing plates

[coopermosley]

I have a few questions regarding the rupes 21 markII, I know that some people put a 5" backing on the 21 to use the 6" pads, but what i was wanting to know is that how practical is actually doing this? does it throw off the balance of the machine or cause additional vibrations? or put stress on the motor and the bearings? If it does, I would rather not risk it and cause premature failure. Also, does anybody recommend the kamikaze backing plates?

[Mike@ShineStruck]

I have a few questions regarding the rupes 21 markII, I know that some people put a 5" backing on the 21 to use the 6" pads, but what i was wanting to know is that how practical is actually doing this? does it throw off the balance of the machine or cause additional vibrations? or put stress on the motor and the bearings? If it does, I would rather not risk it and cause premature failure. Also, does anybody recommend the kamikaze backing plates?

Putting a factory 5in BP on the 21 yes, balance will be off, how much? i dont know as I dont have that combo.
as for the Kamikaze plate, they were made for the purpose of keeping balance and improving rotation speed.

I know I passed on the old design due to it being solid Aluminum..to me it sounds like the plate wouldn't dissipate heat well, aiding pad delamination..
I think the velcro is old tech too.

New design now has venting holes..not sure which velco hook design they use now..if its J hook or Micro hook or w.e

[Mike Moore]

I have a Rupes LHR 21ES Big Foot Random Orbital Polisher (original model) and a Rupes BigFoot LHR15 MarkII Random Orbital Polisher.
I have a 5" backing plate on both machines. I have been using the 5" BP along with the KB washer mod on the 21 since it first came out.
The 21 with a 5" BP is my go-to machine. I've used it for hours & hours for many years with no issues and no noticeable off balance feel.
I feel the the 5"-5.5" pads offer smoother control and better handling. IMHO the 21 throw with a 5" pad is perfect for safe correction work.

[voxbox]

Hi everyone, first post so please be gentle I was given an LHR21 mk2 for christmas(my fiance is nine kinds of awesome) and have read/heard about this 'mod' - is it as simple as unbolting the 6" bp and bolting-on the 5"(from the mk2 i believe)? Sorry if the question sounds redundant, just wanting to be sure

[coopermosley]

Yes that's all you have to do. I tried the 5" backing plate on the 21 yesterday and it did have some additional vibrations, but was still very effective.


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[futurepro17]

Yes, just swap out the 5" backing plate. I tried this combo a few weekends ago and felt it provided better control, slightly more vibration. Use mine with the BOSS thin pads.

[Mike Moore]

NOTE: I have done the Kevin Brown washer mod on the MKII.
However...

They did CHANGE the shape of the area where the KB washer goes on the MKII.
(My guess is Rupes didn't appreciate KB's 5 cent modification to their machine)

The MKII washer area is more rectangle. The KB mod works but you need a slightly different "washer".
In my case, I used a small piece of rectangle metal. I used a grinder to make it fit and drilled a hole in it.
The KB "free spinning" backing plate principle works but I changed the design of the regular round washer.

[voxbox]

Awesome, thanks for the advice everyone