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From: Snag <Snag_one@msn.com>
Newsgroups: rec.crafts.metalworking
Subject: Re: Broaching , a question
Date: Thu, 28 Mar 2024 21:02:23 -0500
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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