Re: Broaching , a question

On 27/03/2024 18:55, Snag wrote:

On 3/27/2024 12:42 PM, David Billington wrote:

On 27/03/2024 17:25, Snag wrote:

On 3/27/2024 9:53 AM, David Billington wrote:

On 26/03/2024 20:40, Snag wrote:

On 3/26/2024 12:58 PM, David Billington wrote:

On 26/03/2024 16:42, Snag wrote:

I'm getting ready to broach my first keyway with an actual broach . My question is about the shims , and how thick they need to be . Measuring the difference between the first and last tooth on the broach I get .062" and I'm wondering if that is the correct thickness for the shims .

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Is it a shop made broach or bought. All my Dumont broaches come with appropriate shims to cut the keyway to the correct depth.
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  It's a couple of broaches only from eBay . I machined a guide slug for it from some 416 SS I bought to "have some on hand in case I need it" and pushed it with my 12/20* ton HF press . I made shims from some .050"  galvanized sheet I have on hand (being a Pack Rat is often a Good Thing) and it worked out quite well . I'll never broach another keyway on the lathe ...
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  *12 ton frame with a 20 ton air operated jack on it . I have beefed up the frame where it was necessary .

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Maybe some of the information in the Dumont catalogue would be of use. It gives the broach lengths and the thickness and number of shims required. https://kar.ca/pdf/catalog/en/Dumont_Catalog.pdf
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  I figure the shim should be the same thickness as the difference between the first and last tooth - mine measure .062 . This will keep the "pilot" on the end in contact with the bottom of the groove being cut . I noticed a variation in the depth on that keyway I cut yesterday ... I think because the broach was not bottomed out in the groove in the pilot bushing .

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I've seen that with mine before like yesterday where the top of the broach was leaning towards me a bit, cutting edges forward, so I corrected it for the second pass for a 4mm key. I'll check my broaches tomorrow and see how the shim thickness correlates to the height increase along the broach and report back.
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  This was a case of I started the cut on the lathe , cranking the carriage forward and back . I think the taper would have self-corrected if I'd used a .062" shim instead of the .050" .

This is what I measured.
Broach list Dumont No 10 set
Size    Start     End     Diff    Teeth     /Tooth    Shim
1/8"    0.390    0.421     0.031    16    0.0021    0.031 x 1
3/16"    0.377    0.429    0.052    16    0.0035    0.050 x 1
1/4"    0.587    0.651    0.064    22    0.0030    0.062 x 1
3/8"    0.569    0.633    0.064    22    0.0030    0.062 x 2
The /Tooth is Diff /(Teeth - 1) . Looks like your original assumption about the shim thickness is correct.