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Loose set/grub screws question

Joined
Feb 16, 2021
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Location
Morristown, NJ
I just bought a Famag Forstner bit extension. Very heavy and apparently well made. It has 4 grub screws to hold the bit. Of course, I tightened all the grub screws before using. On my first use, I found one had loosened, so I re-tightened it. Second use, I lost a screw in the wood dust. Really tightened the rest of the screws. After the next use I now have one screw left.

Next step - I ordered more grub screws on Amazon.

So, my question is, what can I use to keep the screws tight? Something like Loctite won't work as I have to be able to unscrew each time that I change a Forstner bit.

Thanks,
David
 
Joined
Feb 28, 2019
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Location
Kingman, AZ
Grind a flat spot on the fostner bit shank, where the screws touch.
Also, is the fit between the extension and the bit shank snug?
If it is a sloppy fit the movement may be the cause of the screws loosening.
 
Joined
Feb 16, 2021
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Mike - I have to unscrew and tighten the screws multiple times in one session. Loctite won't work because it takes a day to dry after application, and then after each time you unscrew, you have to reapply the Loctite.

Checking Loctite on Amazon brought me to this product. It's closer to what I need, but apparently needs reapplication after "up to 5" uses.

Jim - Good point. The fit is slightly sloppy. Grinding a flat on the shank might help keep the bit from rotating (although I don't remember having a problem with the bit rotating before). Maybe it will help with loosening screws? Anyway, it can't hurt to try that.

Thanks.
 
Joined
Sep 19, 2023
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Location
Columbia, TN
I just bought a Famag Forstner bit extension. Very heavy and apparently well made. It has 4 grub screws to hold the bit. Of course, I tightened all the grub screws before using. On my first use, I found one had loosened, so I re-tightened it. Second use, I lost a screw in the wood dust. Really tightened the rest of the screws. After the next use I now have one screw left.

Next step - I ordered more grub screws on Amazon.

So, my question is, what can I use to keep the screws tight? Something like Loctite won't work as I have to be able to unscrew each time that I change a Forstner bit.

Thanks,
David

Not to change the subject, but this magnet from Amazon is pretty good. It has a plunger on it. Pull the plunger out to turn the magnet "off". I'm not sure how it works, but it does.
 
Joined
Dec 5, 2015
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Seattle, WA
Is the set screw tightening onto a hardened surface? That can be a problem. You might try brass tipped set screws. It helps to have a little distortion of the tip to make it hold better. Grinding a flat for the set screw to tighten onto would be good too.

Some vibration prone applications use double set screws. Tighten the first one then use another one to tighten onto the first one.

What does the seller have to say about this? Send it back. I'm not big on purchasers having to fix tools they paid good money for.
 
Joined
Aug 14, 2007
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Eugene, OR
I guess it would depend on how deep the threaded hole is and how long the set screw is, but I have seen some situations where you secure the first screw, and then tighten up another one on top of it, so a double lock maybe. Never thought of the hammer solution, and I have hammers of many sizes.... As a black smith said, "it is a polyhammerous thing."

robo hippy
 
Joined
Jun 10, 2023
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Sydney, Nova Scotia
I guess it would depend on how deep the threaded hole is and how long the set screw is, but I have seen some situations where you secure the first screw, and then tighten up another one on top of it, so a double lock maybe. Never thought of the hammer solution, and I have hammers of many sizes.... As a black smith said, "it is a polyhammerous thing."

robo hippy
He has to loosen and retighten the set screws every time he changes the bit though. So he would have to completely remove the top four set screws and loosen the bottom four, then reverse the process, every time. I'm still voting for teflon tape, reapplied every once in a while as necessary.
 
Joined
Jul 27, 2020
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Durham, NC
I’m sure you can find these from other sources, but McMaster-Carr have these in any size and thread you could want.
Set screws with thread locker. Sometimes referred to as nyloc.
IMG_1539.png
 
Joined
Dec 5, 2015
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Location
Seattle, WA
STOP THE NONSENSE.......

A a buyer you are not obligated to fix defective items. Stop payment through your credit card. Inform the seller the item in question is at your location and you will return it at their expense. I note this seller's eBay listing says they do not accept returns (that should have been a red flag). Inform the seller they will be receiving a bad review of them and their product.

I see this on too many forums these days. Purchased items don't work correctly. Then the buyer proudly shows how smart he was and how he fixed it. All that does is encourage sellers of poor quality merchandise. Some of this seller's items say made in Germany, unusual, defective items are most often 3rd world.
 
Joined
Feb 16, 2021
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Location
Morristown, NJ
STOP THE NONSENSE.......

I note this seller's eBay listing says they do not accept returns (that should have been a red flag).

HI, Doug - I'm not sure where you're coming from. I didn't buy the extension on EBay. I bought it on Amazon. I could return it easily if I wanted to, but, other than the loose screws, it's very well built. Much better than the last one I had (and my old one had a missing screw also).

I'm going to try Teflon tape first. If that doesn't work, I'll try the ding method. I'm also going to at least start out by putting some duct tape over the screws, so that if they loosen, at least I won't lose them again.
 
Joined
Dec 5, 2015
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Location
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HI, Doug - I'm not sure where you're coming from. I didn't buy the extension on EBay. I bought it on Amazon. I could return it easily if I wanted to, but, other than the loose screws, it's very well built. Much better than the last one I had (and my old one had a missing screw also).

I'm going to try Teflon tape first. If that doesn't work, I'll try the ding method. I'm also going to at least start out by putting some duct tape over the screws, so that if they loosen, at least I won't lose them again.
My point is it's defective if the set screws keep coming loose.

Return it. Return-wise it's better that it came from Amazon. Still, I find it interesting their eBay ads say no returns.

Other than the loose screws it's very well built. Huh???

If the screws keep coming out it is not usable.

So many of our tools, etc come from online sellers these days and I find it irritating that consumers put up with defective items. At very least the seller should be contacted about the problem. You aren't doing future buyers any favors by not bringing this problem to the seller's attention. Who knows knows, maybe they produced a large run of defective ones and they don't even know it.
 
Joined
Jan 10, 2024
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Location
Bournemouth, UK
Unless you’re using small Forstner bits maybe you don’t need to use socket set (grub) screws. If you use suitable length cap head socket screws they have a larger hex socket so you can apply more pressure. It may just make the difference?

IMG_9779.jpeg
 
Joined
Jan 10, 2024
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Location
Bournemouth, UK
Damaging threads will not stop the loosening since the threads will be straightened the first time you thread it in.
Yes, good point. I think it was a bad idea anyway. You can buy thread lock for cycles that temporarily locks screws in place.
I’ve used it on my bike and it works well.
 
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