Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Snag Newsgroups: rec.crafts.metalworking Subject: Re: Broaching , a question Date: Thu, 28 Mar 2024 21:02:23 -0500 Organization: A noiseless patient Spider Lines: 72 Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Injection-Date: Fri, 29 Mar 2024 02:02:21 +0100 (CET) Injection-Info: dont-email.me; posting-host="667e167a8afdb690db5651f084746ddf"; logging-data="4133391"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX19lHJ1Goz7/lEN2JAxtWjtEFdB50n84uNw=" User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.9.1 Cancel-Lock: sha1:5Pc3fVdj4eUD6lBFNVBkZSYCpdU= In-Reply-To: X-Antivirus-Status: Clean X-Antivirus: Avast (VPS 240328-4, 3/28/2024), Outbound message Content-Language: en-US Bytes: 4792 On 3/28/2024 5:19 PM, David Billington wrote: > 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 . >>>>>>> >>>>>>> Is it a shop made broach or bought. All my Dumont broaches come >>>>>>> with appropriate shims to cut the keyway to the correct depth. >>>>>>> >>>>>> >>>>>>   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 ... >>>>>> >>>>>>   *12 ton frame with a 20 ton air operated jack on it . I have >>>>>> beefed up the frame where it was necessary . >>>>> >>>>> 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 >>>>> >>>> >>>>   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 . >>> >>> 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. >>> >> >>   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. > > Thanks for getting back with that info . It seemed intuitive , but ya never know . Now we know . -- Snag "They may take our lives but they'll never take our freedom." William Wallace