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Forstner bit not actual size

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Forum topic by lateralus819 posted 02-27-2014 12:57 AM 1118 views 0 times favorited 13 replies Add to Favorites Watch
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lateralus819

2236 posts in 1351 days


02-27-2014 12:57 AM

So i’m in the making of a chute board. Wanted to use dowels for alignment of the 45 degree and donkey ear attachments.

I used a 3/8” forstner bit out of my PC kit. Couldn’t figure out why there was slop in the dowel. Tried a regular bit, just to see if my suspicion was correct, and it was. It seem’s the forstner bit is maybe a 32nd off.

Has anyone experienced this before? Now I’m wondering if this kit is even good anymore heh.

I have not checked all of them to see if it holds true for all. Luckily i only paid $20 for the set.


13 replies so far

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Don W

17960 posts in 2029 days


#1 posted 02-27-2014 01:13 AM

hah, somewhere I have a blog about the same problem. I wound up using 1/2” dowels. I thought I was loosing it. I probably was but that’s another blog!

-- Master hand plane hoarder. - http://timetestedtools.net

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lateralus819

2236 posts in 1351 days


#2 posted 02-27-2014 01:27 AM

Why 1/2” dowels??

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Don W

17960 posts in 2029 days


#3 posted 02-27-2014 01:39 AM

its what I had bigger than 3/8”

-- Master hand plane hoarder. - http://timetestedtools.net

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lateralus819

2236 posts in 1351 days


#4 posted 02-27-2014 01:46 AM

Oh, i figured wasn’t sure. Yeah with the regular drill bit, it had a nice hammer tight fit! lol.

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bondogaposis

4024 posts in 1813 days


#5 posted 02-27-2014 01:47 AM

Probably because the bit was made overseas and the bit may have been metric and got put in the wrong box or somebody said “close enough”.

-- Bondo Gaposis

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lew

11336 posts in 3217 days


#6 posted 02-27-2014 02:13 AM

I’ve also noticed a difference in dowels from the Borg. Hardwood dowels are pretty close to their stated size but softwood dowels are undersized.

-- Lew- Time traveler. Purveyor of the Universe's finest custom rolling pins.

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lateralus819

2236 posts in 1351 days


#7 posted 02-27-2014 02:18 AM

I tried two different dowels. Both in the forstner hole and the regular drill bit. Both dowels fist nice and tight in the regular bit hole.

If i had other sized dowels i’d check the others.

View gfadvm's profile

gfadvm

14940 posts in 2151 days


#8 posted 02-27-2014 02:25 AM

My PC Forstner bits all seem to be sized correctly when I use them in the drillpress. Not so with the hand held drills.

-- " I'll try to be nicer, if you'll try to be smarter" gfadvm

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RogerInColorado

321 posts in 1416 days


#9 posted 02-27-2014 06:45 AM

I have experienced 3/8 dowels in poplar from the borg being under sized, oak from the borg being over sized, and walnut from Woodcraft being such a perfect fit that it boarders on sweet. I don’t think enough of these vendors use measuring tools that have any accuracy criteria. I think my Stanley tape measure is more accurate than some of the stuff they are using. My PC forstners are dead on, but I’m shocked by that.

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wseand

2754 posts in 2503 days


#10 posted 02-27-2014 08:32 AM

Did you use a caliper to see if it was off.
Sometimes when i drill with Forstner bits they might have a little wobble in them for some reason and it throws off the hole..
Maybe the wood moved a little or something else not sure, but I have the PC bits and 99% of the time they work great.

-- Bill - "Freedom flies in your heart like an Eagle" Audie Murphy

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lateralus819

2236 posts in 1351 days


#11 posted 02-27-2014 11:15 AM

No, my calipers are broke. I’ll do more testing tonight.

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Whiskers

389 posts in 1488 days


#12 posted 02-27-2014 12:35 PM

I have a PC forstner bit set, and use the 3/8 more than any other size cause I like to countersink my screws and use plugs over them, both the mushroom type and the flush type. The bit has been dead on in all cases, but I have always used my drill press for this purpose and my plugs came from woodworkers supply, not the big box stores. For doweling applications I would use normal twist bits anyway, not forstner. Woodworkers supply is the cheapest vendor I have found for plugs, dowels, etc, and their shipping charge is usually only $5 a order. I bought a supply of various plugs and dowels sometime back so have several years worth of stock.

Interesting note if you live in the country, store your plugs and dowels etc in a hard plastic type box, I discovered quite quickly (fortunately) that mice seem to love to munch on them for snacks.

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darthford

532 posts in 1385 days


#13 posted 03-02-2014 06:51 PM

Don’t get me going on the poor quality Asian tools I just purchased a like 21/64 bit the other day which in 64th’s you would think it would have to be accurate, it was ground so off center it was impossible to drill with. It would be straighter if I bent it with a hammer. Ditto for a 6” and 12” hex drive extensions you could watch the tip wobble like a wet noodle.

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