# Lathe slotting attachment



## DPittman (Nov 7, 2019)

Here's a picture of my version of a slotting device for my little lathe.  I line bored and reamed the cylinder shaft on my lathe to ensure it was in line and perfectly centered with my lathe.  The shaft was a repurposed shaft from a strut (I believe) and I found it pretty hard to mill with my little lathe (just had to do the slot in the side of the shaft).  I modified a few different boring bars for it for different size of bits/slots.


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## Janger (Nov 7, 2019)

So how / where do you mount this device Don? On the cross slide? I have a motor mount that needs a keyway. Your looks efficient.


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## DPittman (Nov 7, 2019)

Janger said:


> So how / where do you mount this device Don? On the cross slide? I have a motor mount that needs a keyway. Your looks efficient.


Yes mounts on cross slide.  I have cut a slot with my lathe before with just a tool bit in a holder and using the carriage to move the bit back and forth.  For just a bit of slotting I think this is okay but the separate attachment eliminates the extra wear and tear and stress on the carriage components.  However it ain't no production machinery! As it is slow and tedious (especially in steel). I


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## Janger (Nov 7, 2019)

yep that’s a good way. If you don’t have a broaching setup and need an internal keyway what other options are there? I would like to know if there is another solution. .. anyone?


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## kylemp (Nov 8, 2019)

It more or less has to be a single point operation, so it has to generally be a broach or shaping operation. There are 90 degree heads that can be put inside a bore with a small rotating cutter to accomplish a keyway but you'd need a very large bore before you could use something like that. 

This has made it onto my "to make eventually" list as it would be a lot more dynamic in the sense of not needing a bunch of very expensive broaches to cover standard sizes, not to mention plugs and shims.


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## Brent H (Nov 8, 2019)

Depending on the length of shaft or bore I have had success by off setting the blank and boring a pilot hole for the key and then using the tool post approach to finish the square sides on the key way.  I did this for the pulley I made for my lathe.  Takes some advance prep to pre-drill.  Can also relieve out on the mill with a proper sized end mill to plunge in a relief and then square up with a file or on the lathe.  You could also offset drill on the drill press - fit a plug in the bore to keep drill aligned.


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## historicalarms (Nov 8, 2019)

I do have a small (up to 1/4") broach cutting set purchased on a whim "that I might just need that some day" and I have used it a few times but most of the time I need something bigger and a "custom sized" single use broach can be made very cheaply in an hour or so with a piece of appropriately sized high speed steel cutter blank, a bench grinder or sander to cut the initial side angle and a Dremmel to cut 3 or 4 biting teeth. Incidentals needed are a bit of slotted "guide" shafting and a hyd press to push it through. 

    The "biting teeth" can be, but don't need to be relieved deep enough to contain all the cuttings in one push as most workpieces we have to slot can be turned over. The broach can be pushed a bit until you think the "relief" area is full, then turned over, pushed out, cleaned, turn back over and start again...it works, I've done it a couple of times. I use a shop 20 ton press now but the first time I did this I used 2 fire bricks under the workpiece for clearance for the broach to be pushed into and a 4 ton bottle jack for a power source. I set the whole issue up under a 1 ton pickup bumper for a "pressure point" anchor....sure was a mickey-mouse set-up but it worked.

     Actually home made "single point" broaches have been used by "home shop, kitchen table gunsmiths for years (since the 1840's that I know of) to cut rifling in gun barrels and if they could do it with their equipment that far back we should be able to do just as good a job with ours now.  Two of the best "cut rifling" barrel makers in the world right now are both in Ab. and both use their own home-built rifling cutters. 

    It sure is interesting how a visit to Ron's grainery/shop 30 years ago could solve a problem a couple years ago...I remember thinking, when I built the first broach cutter I needed, that if Ron can cut rifling that will hit a postage stamp at 500 yrds then I sure as he!! can cut a groove to turn a gear hub.


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## Janger (Nov 9, 2019)

That is a fancy Slotting tool. 60 build videos he has! 


historicalarms said:


> I do have a small (up to 1/4") broach cutting set purchased on a whim "that I might just need that some day" and I have used it a few times but most of the time I need something bigger and a "custom sized" single use broach can be made very cheaply in an hour or so with a piece of appropriately sized high speed steel cutter blank, a bench grinder or sander to cut the initial side angle and a Dremmel to cut 3 or 4 biting teeth. Incidentals needed are a bit of slotted "guide" shafting and a hyd press to push it through.
> 
> The "biting teeth" can be, but don't need to be relieved deep enough to contain all the cuttings in one push as most workpieces we have to slot can be turned over. The broach can be pushed a bit until you think the "relief" area is full, then turned over, pushed out, cleaned, turn back over and start again...it works, I've done it a couple of times. I use a shop 20 ton press now but the first time I did this I used 2 fire bricks under the workpiece for clearance for the broach to be pushed into and a 4 ton bottle jack for a power source. I set the whole issue up under a 1 ton pickup bumper for a "pressure point" anchor....sure was a mickey-mouse set-up but it worked.
> 
> ...



I’d love to see some pictures of these shop made broaching tools you fab up. care to post more?


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## Dabbler (Nov 9, 2019)

cam at battler is one of the really good ones.


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## YYCHM (Nov 9, 2019)

Is this essentially a one degree manual shaper?


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## Dabbler (Nov 9, 2019)

one degree?  it is a shaper with side to side control via the carriage.  Up/down control is more difficult, and is done by set up.  same as a manual shaper that mounts where the compound would go. still does the job very well.


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## historicalarms (Nov 10, 2019)

Janger said:


> That is a fancy Slotting tool. 60 build videos he has!
> 
> 
> I’d love to see some pictures of these shop made broaching tools you fab up. care to post more?



   I will look for one but can't promise anything LOL. things I build in the shop sometimes get re-purposed into different shaped cutters on occasion.

     really quite easy to "visualize tho... an inch or so length of appropriate sized high speed steel and grind a 4 or 5 thou slope from end to end on one side  and then cut 3 or 4 grooves crossways with a "positive angle cutting edge at the large end of each groove...just picture a commercial broach that is 4 inches long shortened to an inch and with no "side clearance cuts that they have.

    you could make the 'slope grind any graduation that can be handled in the cutting action by your hyd press.


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## Janger (Nov 10, 2019)

Tubalcain demonstrating the lathe based method of internal broaching.


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## PeterT (Nov 10, 2019)

I like Don's device. The lever has lots of mechanical advantage. Maybe one could make a base plate that supports a chuck vertically. This way the vertical center height of part will always coincide with the broach ram. That just leaves one issue - a way to increment the broach head a little bit between strokes. Making it increment up & down would be involved, horizontal would be easier. In the lathe setting, the cross slide is doing this action. Maybe a 1-axis mill table, or replicate that movement with a feed screw?

The only thing that makes me apprehensive about broaching in the lathe is axially hitting the spindle bearings every stroke. I doubt it would be a problem for light cuts, but maybe heavier steel or CI? If the tool was divorced from the lathe one could get a bit more rammy. I guess that's why shapers are so robust or in the case of of broaching, hydraulic presses. But nibbling away at it seems like a good method if you aren't in production.


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## Dabbler (Nov 10, 2019)

These broaching operations can only take very tiny depth of cuts:  usually .003 or so...  Yeah, it is an impact, but the impact of a tool on the end of a shaft taking a heavy cut is more force on the bearings than broaching...


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## PeterT (Nov 10, 2019)

Good to know. Lathe is easier then.


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## Dabbler (Nov 10, 2019)

Bert always borached keyways on his mill using the quill.  To each his own.  If you get 3 machinists in a room, you have 6 ways to do any operation.


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