Harman exhaust stub, impossible to drill for attaching stove adapter?

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Jan 29, 2021
149
VA, east central
The installation manual for the P68 states that three screws should be used to fasten the stove adapter to the exhaust stub, and while I'm sure you can get it done, I'm not sure what type of drill bit you'd need to do that. I tried last night with a high speed titanium coated 1/8" bit and made it through the adapter wall easily, but failed to do more than slightly dimple the exhaust stub itself. Harman supplied two galvanized self-tapping sheet metal type screws (where was the third?) for which I'm assuming is for attaching the stove adapter, but they could hardly mark the stub wall. Anybody know what type of metal it is? I'm guessing some type of cast iron? Anybody successfully drill their P-series exhaust stubs? What kind of bit did you use?

Anyway, I ended up just using high temp RTV silicone on the inside of the adapter followed by several wraps of high temp silicone sealing tape. Seems to be doing just fine.
 

Washed-Up

Minister of Fire
Nov 5, 2011
800
Kananaskis,Alberta, Canada
I used cheap self tapping screws and they went through fairly easy
 
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Washed-Up

Minister of Fire
Nov 5, 2011
800
Kananaskis,Alberta, Canada
That’s on 2 P61a’s and an older pellet pro 2 Harman. These are what I used
 

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Pete Zahria

Minister of Fire
Jan 6, 2014
1,205
New Hampster
mcmanusfuels.com
That’s on 2 P61a’s and an older pellet pro 2 Harman. These are what I used

Me too. self tappers, work.
2 stoves.. no problem
(I use the hex head ones...)

Not all.. but many of those gold colored drill bits,
are more suited for drilling soft butter..


Dan
 
Jan 29, 2021
149
VA, east central
Weird. The self tappers that came with the stove, nor the stainless replacements I bought didn't do anything using moderate pressure. Maybe I need my A/C power drill vs battery drill. Although it has a decent high end rpm.

The high temp sealant combined with high temp silicone tape seems to be working just fine, although I know that screw are more secure.
 

SciGuy

Feeling the Heat
Aug 17, 2007
310
Constableville, NY
The installation manual for the P68 states that three screws should be used to fasten the stove adapter to the exhaust stub, and while I'm sure you can get it done, I'm not sure what type of drill bit you'd need to do that. I tried last night with a high speed titanium coated 1/8" bit and made it through the adapter wall easily, but failed to do more than slightly dimple the exhaust stub itself. Harman supplied two galvanized self-tapping sheet metal type screws (where was the third?) for which I'm assuming is for attaching the stove adapter, but they could hardly mark the stub wall. Anybody know what type of metal it is? I'm guessing some type of cast iron? Anybody successfully drill their P-series exhaust stubs? What kind of bit did you use?

Anyway, I ended up just using high temp RTV silicone on the inside of the adapter followed by several wraps of high temp silicone sealing tape. Seems to be doing just fine.

I've always imagined that the screws were to go through the adapter and press against the exhaust stub but not penetrate it. None of the used stoves I've worked on ever had drilled exhaust stubs. I have just used high temperature foil tape and or silicone tape and foregone any screws. Not saying that this is gospel but it's my experience.

YMMV,

Hugh
 
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Pete Zahria

Minister of Fire
Jan 6, 2014
1,205
New Hampster
mcmanusfuels.com
Personally, I don't think they need to be screwed in, either.
I think the stretchy silicone tape is adequate.. so little stress on that connection.
On my own.. one self taper goes in so easy, I just do it.
However, I NEVER use RTV on ANY of the joints..
Brutal if not impossible to get the joints apart later..


Dan
 
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Harman Lover 007

Minister of Fire
I’ve never attached my adapter to either of my stoves. Never had a problem or a leak......
 
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tlc1976

Minister of Fire
Oct 7, 2012
905
Northwest Lower Michigan
I just siliconed mine, no screws. Just a 45 and straight out the wall and outside it is bracketed. It can’t move.

If I had a long section in the house, I would use screws.
 
Jan 29, 2021
149
VA, east central
I've always imagined that the screws were to go through the adapter and press against the exhaust stub but not penetrate it. None of the used stoves I've worked on ever had drilled exhaust stubs. I have just used high temperature foil tape and or silicone tape and foregone any screws. Not saying that this is gospel but it's my experience.

YMMV,

Hugh
Pretty sure screws are intended to penetrate stub as well. There's not enough material, or thickness, in adapter wall for threads to bite and hold. Plus, other complications.
 
Jan 29, 2021
149
VA, east central
Personally, I don't think they need to be screwed in, either.
I think the stretchy silicone tape is adequate.. so little stress on that connection.
On my own.. one self taper goes in so easy, I just do it.
However, I NEVER use RTV on ANY of the joints..
Brutal if not impossible to get the joints apart later..


Dan
For this connection, I don't imagine RTV to cause a problem on removal b/c the stub has a slight taper and adapter doesn't have a nice snug fit on it's own. Otherwise, yeah this would be a problem removing.
 

rich2500

Minister of Fire
Nov 19, 2005
1,393
Berks County PA.
My concern with not having screws in would be that in the event of a violent ignition ( when the firebox fills with heavy smoke before igniting and then finally ignites and an explosion occurs in the firebox ) this could possibly blow the exhaust off the stove. Had one of those violent starts with my Serenity and other then making a major mess inside the stove no other issues but there have been reports of blowing glass out of stoves. Better to be safe then sorry
 
Jan 29, 2021
149
VA, east central
My concern with not having screws in would be that in the event of a violent ignition ( when the firebox fills with heavy smoke before igniting and then finally ignites and an explosion occurs in the firebox ) this could possibly blow the exhaust off the stove. Had one of those violent starts with my Serenity and other then making a major mess inside the stove no other issues but there have been reports of blowing glass out of stoves. Better to be safe then sorry
Wow, blowing glass out? Screws definitely would keep it in place and would be ideal safety wise. But if RTV and silicone tape can't secure the connection, then you probably have other problems, especially if glass gets blown out. I'd imagine this only happens if stove isn't maintained and vent fills with fly ash?
 

SidecarFlip

Minister of Fire
Feb 7, 2010
5,273
S.E. Michigan
Right, that makes sense. I did try lower speed too. I think I just have lousy bits.
I think you do too. Gold colored 'Titanium Nitride' don't mean squat, all it does is promote good chip flow and cheap bits are just that, cheap. Could be a dull bit too. Bet you don't know how to sharpen a twist drill.... I do.

Go to MSC and buy yourself a set of quality American made twist drills, like Chicago Latrobe or Cleveland Twist or Triumph. They ain't cheap but good stuff is never cheap. Only cheap stuff is cheap,

Having said that, I've never screwed my venting to the exhaust stub but here is what I do...

I take a thin kerf cutoff wheel in my battery operated 4.5" angle grinder and I cut the galvanized outer jacket from the venting just past the crimped in part, exposing the stainless inner pipe. Then I coat the inside of the inner pipe and the outside of the exhaust stub with high temp (red) rtv and slip the stainless steel inner pipe over the stub and put on a Witek (worm clamp) and cinch it down. Been doing it that way for decades. No leaks whatsoever.
 

SidecarFlip

Minister of Fire
Feb 7, 2010
5,273
S.E. Michigan
My concern with not having screws in would be that in the event of a violent ignition ( when the firebox fills with heavy smoke before igniting and then finally ignites and an explosion occurs in the firebox ) this could possibly blow the exhaust off the stove. Had one of those violent starts with my Serenity and other then making a major mess inside the stove no other issues but there have been reports of blowing glass out of stoves. Better to be safe then sorry
Been fiddling with this stuff for over 25 years and never heard of that happening.
 
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SidecarFlip

Minister of Fire
Feb 7, 2010
5,273
S.E. Michigan
Sidecar are you bragging or complaining :)
I also know how to sharpen a twist drill
Neither. As a retired tool maker one of the first things I learned was how to offhand sharpen a twist drill and relieve the heel for better cutting. You'd be surprised how many people haven't a clue how to properly split the webs, apply the clearance and grind them so both flutes cut evenly.

Most people when a drill gets dull, just push harder and hope and when it breaks or gets so hot it looses it's hardness, just toss it and chuck a new one. Probably why people buy the cheap ones. Who wants to drop 10 bucks on a drill that they know they cannot do squat with once it's dull. Then there is the guy who spins a drill backwards and wonders why it won't cut.

All my friends bring me their drills to get sharpened, none of them have a clue.

My issue now is, it's hard for me to do the little ones. I cannot see them well. .500 or better, no issue, even .250. below that I start having issues and below .125 it really gets to be an issue. I prefer parabolic twist drills myself, they cut better and chip flow is better but they require a special sharpening technique.

I like the really BIG ones over 1.5". I sharpen them on a flat faced 15" abrasive disc instead of a bench wheel. I can reef on them without taking the hardness out.

My drill indexes, all of them, Number, letter and fractional, and metric, all have various length drills in them. OAL will depend on how much I use a size because I tend to resharpen after every use. When they get too short, I buy a new one., I like to have at least 1" of flute left.

The used up ones make good center punches too.

I have a Darex but I rarely use it. It's the big buck one. Bought it at a machinery auction years ago. Thought it would be quicker and better. neither held true.
 

rich2500

Minister of Fire
Nov 19, 2005
1,393
Berks County PA.
Been fiddling with this stuff for over 25 years and never heard of that happening.

you replied in that post so you must of forgot about it.

ignition explosion

and another

another

Some of these can be pretty violent depending how much gas builds up in the firebox. It's in the Harman install manual that you need screws into the exhaust stub, now if some one wants to put their family at risk by not following the manufactures install procedure that's their choice.
 
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Washed-Up

Minister of Fire
Nov 5, 2011
800
Kananaskis,Alberta, Canada
I’ve had the “POOF” a few times and found either under the burnpot where the igniter is had too much gunk/fines in it, the burnpot holes needed a little hone of the holes(carbon buildup) or damp pellets. I believe Sidecar as he’s VERY anal about how clean his stove is...but I’ve seen the posts here before....unique circumstance to have an ignition that big though I’d think.....extremely dirty would be my first guess
 

SidecarFlip

Minister of Fire
Feb 7, 2010
5,273
S.E. Michigan
I see I did, long time ago.... I imagine you could build up an explosive atmosphere though I never have in mine but mine is a manual start and I don't use a lot of pellets to start it and there is always a flame present, soon as I light the pellets. I do get some smoke but not much.

Now, I remember the whoosh (not really an explosion), more like a 'puff' when I lit off my coal furnace back in the day. I used to call it the 'coal puff'. from the unlit smoke the coal was putting off.

I have to say that the other day I actually had some vapor coming out of the FAK when I lit the pellets. I'm not using starter jell, I'm using charcoal liquid starter I soak the pellets in. Had the door open and the draft fan on high as I was dumping the transition Tee on the outside. Didn't go whoosh so all was good.

Don't believe I could physically blow the vent off the stub. it's on there really good and secured with a Witek clamp and sealed with red RTV. Mine ie a straight shot through the the outside wall to the 3-4 transition Tee and vertical 18 feet. The transition Tee as well as the vertical sections are secured to the outside house wall with stand off's I fabricated from 1/8" hot rolled plate and 1 x 1/8" hot rolled steel strip, all welded together. Nothing moves inside or outside, very rigid. Didn't care for the Simpson stand off brackets, just didn't look stout enough to me, but that that is what I do, steel fabrication so I built what I considered to be a substantial mount.

Think it would be pretty hard to blow the glass out of the door. That would take quite a whomp. I wonder (in that thread) if the glass was compromised with a small crack in the perimeter somewhere.

I'm on my second glass. I broke the first one years ago but was my own doing. I had replaced the door gasket and for kicks and grins checked the securement screws that retained the glass. Should not have done that as I compromised it and it cracked so I replaced it.

I only use just enough pellets to start a small fire in the pot and then the corn comes in and off she goes.

Not fond of cal rod ignition and never will be. I much prefer manual start. I realize it's a convenience thing, but not my thing. Just like the hopper lid microswitch. I don't want that either and if I ever bought a new unit, I'd disable that right away.

I may buy another unit for the shop in as much as propane is climbing like a jet on afterburner and I heat my shop all winter.