HG-1 build quality issues - Page 6

Grinders are one of the keys to exceptional espresso. Discuss them here.
User avatar
drgary
Team HB
Posts: 14348
Joined: 14 years ago

#51: Post by drgary »

That seems simple to try. I'll report back.
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

User avatar
drgary
Team HB
Posts: 14348
Joined: 14 years ago

#52: Post by drgary »

I did as Jake suggested, and my grinder is back together with base bolts that easily go all the way in and fasten down well. I chose to fasten them to 15 ft/lbs using a torque wrench. Added: I measured the depth of the hole, and it's 55mm from the bottom of the recess. That means if the cap takes about 10mm, the hole extends 65mm from there. For practical matters, should you want to insert a longer bolt, there are 15mm to spare beyond the 40mm length of the current threaded post.

Here's the aluminum caught in the bolt threads. I was able to get it out pretty easily with that pick. Then I used a wire brush to remove surface rust.



I used a tap to chase the threads and got quite a bit of aluminum filings, which I vacuumed out and tapped out as best I could.





Then I slathered this anti-seize compound over the entire bolt. It went in easily and fastened down well.



Here's the condition of the second bolt. It offered some resistance during removal with my ratchet wrench but less than the first one. I didn't chase the threads but otherwise gave it the same treatment as the first bolt.

Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

OldNuc
Posts: 2973
Joined: 10 years ago

#53: Post by OldNuc »

If you have good threads then a 45ft-lb torque is the specified so if you want to back off a bit 30ft-lb should hold it. The trick to hammering is to use nothing larger than 11-12 oz head weight and first use a 6mm flat nosed punch stuck into the hex and whack it multiple times hard to break the oxide grip. Then use a long hex key and apply a medium hand pressure on the end of the key while striking the key on the long leg close to the short leg entering the bolt. You apply the force to actually turn the bolt, not the hammer. The hammering is to vibrate the molecules sufficiently that the bolt turns.

A 10mm bolt into aluminum requires 2 x the diameter, 20mm, of good thread engagement to hold full torque. You are likely fine here to pull it up a bit if you want.
★ Helpful

User avatar
drgary
Team HB
Posts: 14348
Joined: 14 years ago

#54: Post by drgary »

Thanks, Rich. Regarding amount of torque, I'd like to not make it so tight that it's difficult to loosen the bolts later. 15 ft/lbs seemed about as firm or firmer than what it took to break the 2nd bolt loose. With the grinder back on the counter, the post feels like it's solidly attached. I hesitate to torque it harder unless it loosens. Is there any reason to crank it up to 30 ft/lbs in this case?
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

User avatar
Jake_G
Team HB
Posts: 4295
Joined: 6 years ago

#55: Post by Jake_G »

There is...

No time to get into details right now but imagine a bolt as a fish scale. Hang a 15 lb fish from it (let's pretend you did when you torqued it to 15 ft lbs) and then pop a block into it so it can't go back to zero. You take off the 15lb fish and the scale still reads 15 lbs. Because it's got a block in it, stretching the spring. You follow so far? The base of your grinder represents the block.

Ok now you can hang any fish you want to that weighs less than 15 lbs and the scale doesn't budge. In fact, the spring doesn't even know there's a fish hanging from it because the spring is preloaded to 15 lbs. All the spring ever sees is 15 lbs as long as you dont ever hang a heavier fish from it... if you hang a 16 lb fish from the scale, the spring stretches, the block gets loose and the spring starts experiencing fatigue. Eventually, after enough cycles, the spring fails.


This is why you should size a fastener based on the expected loading and always torque the fastener based on the fastener's clamping load. You pre-stretch the bolt to give you a clamping load that far exceeds any working stress you will actually subject the bolt to and then you can "hang any size fish you want" and the bolt literally never knows the difference between sitting there holding the grinder together or chomping through some crazy light roast.


Sorry for the sporadic metaphor, but I'm short on time.

Cheers!

- Jake
LMWDP #704
★ Helpful

User avatar
Craig Lyn
Posts: 49
Joined: 12 years ago

#56: Post by Craig Lyn »

Hi Guys,

Craig Lyn here. I'm the guy who designed the HG-1. First of all apologies to everyone who might have been having issues with the black oxide alloy steel M8's. In the past, there were some reported issues with the quality of the screws on the bottom of the grinder. There was evidence of surface oxidation in some of the grinders, which while annoying, is only a cosmetic issue.

That being said, we all want our tools to look great. If this bothers you, I'd recommend removing the screw and then applying a little bit of penetrating oil to prevent any oxidation. I've always used a socket wrench to loosen anything difficult. A good tip is if you're having issues removing the screw, apply more leverage and don't bang on it with a mallet. Just put a piece of pipe over the end of the tool and you'll be able to extend the leverage even more.

For those of you who want to swap the M8's with sus, you can easily find them on McMaster.

The original 40mm screw length is a bit overkill, and you can easily use an M8x1.25 25mm. There are 2 dowel pins in the base of the unit as well which gives the back a little bit more rigidity. That's why you don't necessarily have to put more torque on the screws when tightening them.

https://www.mcmaster.com/91292a148

To be honest I never in my wildest dreams would have believed that so many people would have bought one of these grinders, much less have modified them. This wasn't a product that was designed to be taken apart or have a motor attached to it. That being said for those enterprising individuals kudos!

respectfully,

Craig

User avatar
drgary
Team HB
Posts: 14348
Joined: 14 years ago

#57: Post by drgary »

Craig, thanks for joining the thread and giving us more tips and context on your terrific grinder. FYI the model I've been servicing is a 2014 83mm.

Jake, there is ...

One more salient detail. I would think you adjust torque not just for the spec of the fastener, but also according to how easily you want to remove it and how much load you're likely to put on it, true? I think you covered the last part -- how heavy a fish you will put on the scale. There is also the stabilization of the flat bottom of the post fastened to the base.

:?: :shock:
Jake_G wrote:There is...

No time to get into details right now but imagine a bolt as a fish scale. Hang a 15 lb fish from it (let's pretend you did when you torqued it to 15 ft lbs) and then pop a block into it so it can't go back to zero. You take off the 15lb fish and the scale still reads 15 lbs. Because it's got a block in it, stretching the spring. You follow so far? The base of your grinder represents the block.

Ok now you can hang any fish you want to that weighs less than 15 lbs and the scale doesn't budge. In fact, the spring doesn't even know there's a fish hanging from it because the spring is preloaded to 15 lbs. All the spring ever sees is 15 lbs as long as you dont ever hang a heavier fish from it... if you hang a 16 lb fish from the scale, the spring stretches, the block gets loose and the spring starts experiencing fatigue. Eventually, after enough cycles, the spring fails.
a

This is why you should size a fastener based on the expected loading and always torque the fastener based on the fastener's clamping load. You pre-stretch the bolt to give you a clamping load that far exceeds any working stress you will actually subject the bolt to and then you can "hang any size fish you want" and the bolt literally never knows the difference between sitting there holding the grinder together or chomping through some crazy light roast.


Sorry for the sporadic metaphor, but I'm short on time.

Cheers!

- Jake
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

User avatar
HB
Admin
Posts: 21983
Joined: 19 years ago

#58: Post by HB »

wug2grinder wrote:As the inventor of the kit, I would like to express my experience and those opinions I received about this issue.
Craig Lyn wrote:I'm the guy who designed the HG-1.
Given the specifics of the problem under discussion, we'll apply the site's rules on vendor participation in the forums less strictly. But as a reminder, generally speaking, vendors should limit their posts to correcting factual errors to avoid the appearance of "soliciting business under the guise of being helpful".
Dan Kehn

User avatar
Jake_G
Team HB
Posts: 4295
Joined: 6 years ago

#59: Post by Jake_G »

drgary wrote: Jake, there is ...

One more salient detail. I would think you adjust torque not just for the spec of the fastener, but also according to how easily you want to remove it and how much load you're likely to put on it, true? I think you covered the last part -- how heavy a fish you will put on the scale. There is also the stabilization of the flat bottom of the post fastened to the base.

:?: :shock:
Correct,

But in the design phase, you select a fastener such that when torqued to 80% of its capacity, it supports your design load plus whatever factor of safety you want. I usually design between 3 to 5 for a factor of safety to account for instantaneous loads that exceed the normal operating conditions, but I dont design things that fly, where the factor of safety is much lower (bidder equals heavier equals likes to fall out of the sky...).


I have no idea how much bending moment (torque around the joint between the upright plate and the baseplate) the fasteners are subjected to, but you have to assume that the fastener was chosen for a reason, so it should be torqued according to its design specifications, regardless of the application. Any less torque and you run the risk of the fastener coming loose at a best case, and suffering a fatigue or ultimate failure in the worst case...

The fact is, you dont know how heavy a fish you might catch when grinding a light roast, so let's just assume the bolt can catch a 30 pounder and plan accordingly, eh?

Cheers!

- Jake
LMWDP #704

User avatar
drgary
Team HB
Posts: 14348
Joined: 14 years ago

#60: Post by drgary »

Well explained. I'll tighten it up to 30 ft/lbs, as Rich suggested.
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!