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Question About Tool Design

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Forum topic by DaveB48 posted 06-04-2020 10:55 PM 270 views 0 times favorited 7 replies Add to Favorites Watch
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DaveB48

4 posts in 1936 days


06-04-2020 10:55 PM

I am making a turning tool with a round carbide cutter screwed to the end of a square steel bar. In almost all examples of such DIY tools I have seen online, part of the end of the bar is cut away to form a ledge, so that the cutter can be mounted flush with the top surface of the bar. This is also true of commercial tools. Why is this necessary? Why not mount the cutter on the top surface of the bar?

-- Dave in Richmond, IM4 TECH


7 replies so far

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LittleBlackDuck

4673 posts in 1591 days


#1 posted 06-04-2020 11:58 PM



.... This is also true of commercial tools….
- DaveB48

I’m no engineer DB and I often take some YouTube posts with a grain of salt… however, I’m sure manufacturers have sunk counless dollars into R & D to develop an optimum tool…

You gonna question the shape of a wheel?

-- If your first cut is too short... Take the second cut from the longer end... LBD

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MrUnix

8085 posts in 2969 days


#2 posted 06-05-2020 12:01 AM

No idea… but if I had to guess, I’d say it was either to protect the non-cutting edge that faces the operator from accidental contact, or to bring the cutting edge closer to the centerline of the tool.

Cheers,
Brad

-- Brad in FL - In Dog I trust... everything else is questionable

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Nubsnstubs

1723 posts in 2500 days


#3 posted 06-05-2020 02:59 AM



No idea… but if I had to guess, I d say it was either to protect the non-cutting edge that faces the operator from accidental contact, or to bring the cutting edge closer to the centerline of the tool.

Cheers,
Brad

- MrUnix


Keeping the cutting edge near center line would give you better control of the tool. .............. Jerry (in Tucson)

-- Jerry (in Tucson) www.woodturnerstools.com

View HokieKen's profile

HokieKen

14002 posts in 1909 days


#4 posted 06-05-2020 03:01 PM

For one thing, having a pocket for the insert to set in will prevent, or at least minimize, it’s ability to rotate when cutting. Also, carbide inserts are intended to cut on the centerline of the work with the tool held horizontally. For a lot of lathes, if the insert were on top of the bar, the tool rest may not go low enough in the banjo to allow proper use.

-- Kenny, SW VA, Go Hokies!!!

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DaveB48

4 posts in 1936 days


#5 posted 06-05-2020 05:54 PM

Thanks to all, especially Kenny for an insightful explanation. I have completed the metalworking, making the pocket and mounting the round cutter.

-- Dave in Richmond, IM4 TECH

View them700project's profile

them700project

245 posts in 1789 days


#6 posted 06-05-2020 06:40 PM

My thought would be that their square/triangular cutter heads need to be recessed to prevent them from turning and the round just follows along to have a similar look/feel

View OSU55's profile

OSU55

2646 posts in 2760 days


#7 posted 06-05-2020 08:16 PM

2 primary reasons for a ledge for the carbide cutting tool
1) increase tool rest height
2) tool will be more stable with the cutting edge closer to the bar CL, especially when rotating the tool for sheer scraping.

Unless the tool is used overly aggressively, cutter rotation is not an issue IME. Get the “ledge” parallel and perpendicular to the bar CL and you are good to go. I prefer round bars that are easily rotated for more of a sheer cut, but either works. Its better to use a large bar and grind it down to the cutter size at the end – less vibration/chatter.

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