# QCTP Adapter for Micro 100 carbide boring bar



## Janderso (Mar 21, 2021)

These small boring bars are great.
They are a PITA to mount in the holder.
I know Micro sells these and yes I’m sure they look better than mine but it works great.
I’ll either grind down the set screws or leave them alone.
It works just fine as shown.
Drilled and reamed to .001” over size. Fits real good.


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## ttabbal (Mar 21, 2021)

Looks good to me! I might have to make one for my micro tools. Beats trying to mount them in the block directly.


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## Janderso (Mar 22, 2021)

ttabbal said:


> Looks good to me! I might have to make one for my micro tools. Beats trying to mount them in the block directly.


Boy Howdy!


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## mikey (Mar 23, 2021)

Jeff, have you considered making a similar sleeve but putting a compression slot through one side instead of using screws? That would allow you to angle the tool so the tip points a few degrees up to reduce tangential forces.


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## Janderso (Mar 23, 2021)

mikey said:


> Jeff, have you considered making a similar sleeve but putting a compression slot through one side instead of using screws? That would allow you to angle the tool so the tip points a few degrees up to reduce tangential forces.


I hadn't ,
Could you show us an example?

This was just a quick and dirty approach.


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## Cadillac STS (Mar 23, 2021)

Here is a video on making a square hole by Tubalcain which may help with making these..


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## mikey (Mar 23, 2021)

Janderso said:


> I hadn't ,
> Could you show us an example?
> 
> This was just a quick and dirty approach.



Sure, it would look like this:




The advantages are that the entire bar is clamped, not just held by a few screws in a small area, and you are able to alter the rotation of the bar to whatever you deem necessary. Rotating the tip of the bar up by a few degrees amounts to adding back rake; that should focus the cutting forces at the tip of the tool, increase chip flow for better chip egress and reduce chip thickness and reduce tangential cutting forces.

This kind of sleeve is NOT ideal. A better one is like the one Aukai made in this thread because it completely clamps the bar 360 degrees and holds it solidly while also allowing you to alter the angle of the bar at need. Note also that he is using a BXA-4D boring bar holder, probably one of the best bar holders on the market. The 4D will clamp a slitted sleeve solidly and this makes a difference in how well the boring bar performs. 

I think the sleeves sold by Micro 100 and others with two set screws near the tip are designed to allow boring bar changes in a CNC tool holder. It allows them to quickly tailor stick out when swapping out a dull bar. For a manual lathe user, this is not an advantage.


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## jwmelvin (Mar 23, 2021)

mikey said:


> This kind of sleeve is NOT ideal. A better one is like the one Aukai made in this thread because it completely clamps the bar 360 degrees and holds it solidly while also allowing you to alter the angle of the bar at need. Note also that he is using a BXA-4D boring bar holder, probably one of the best bar holders on the market.



I’d like to understand the distinction you are making. The slit-square section seems entirely the same as a slit-circle section. 

Also: you find the -4D holder is significantly better than the -4 holder in rigidity?


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## mikey (Mar 23, 2021)

jwmelvin said:


> I’d like to understand the distinction you are making. The slit-square section seems entirely the same as a slit-circle section.
> 
> Also: you find the -4D holder is significantly better than the -4 holder in rigidity?



The difference is not so much in the cross section of the adapter but in the bar holder itself. Jeff is using a standard tool holder so the slitted holder will support and clamp the bar more solidly than using two set screws on one end to hold the bar. The round adapter Aukai made allows the entire bar to be enveloped and clamped down solidly by the 4D. Essentially, the bar becomes one with the tool holder when this happens.

I absolutely think the 4D is better than the 4. The 4D clamps by compressing a slit so that the entire holder encircles and clamps the bar solidly. In contrast, the 4 uses cotters, much like import holders do, and applies pressure at only two points of the bar; this works but not nearly as well as surrounding and clamping the entire surface of the bar like the 4D does. Moreover, the 4D compresses sleeves just as well.

I made an aluminum boring bar holder for my Sherline lathe that is almost the same as the 4D except mine uses 4 screws instead of two like the 4D has. That bar holder is solid enough to hold a 3/8" carbide bar at max extension taking heavy roughing cuts with zero chatter. The bar holder plus the QCTP that holds it weigh less than an Aloris 4D by itself. With sleeves, it will also hold my tiniest boring bars with no problems so I am sold on the design.


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## Janderso (Mar 23, 2021)

Now I get it.


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## ttabbal (Mar 23, 2021)

I've been thinking about building a 4D style holder for bars. Big block of steel, dovetail for the QCTP, and a good size bore, slit and drill/tap for some clamping screws. Wouldn't be that different from the normal toolholders I made that have been working well.


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## jwmelvin (Mar 23, 2021)

Makes me want to make one too! I’d kind of rather spend the money on a dovetail cutter and make a holder than buy a holder. I’ve also been wondering if I could open my AXA holders to fit my BXA post...


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## mikey (Mar 23, 2021)

Pretty simple to make, guys. Go for it.


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## ttabbal (Mar 23, 2021)

jwmelvin said:


> Makes me want to make one too! I’d kind of rather spend the money on a dovetail cutter and make a holder than buy a holder. I’ve also been wondering if I could open my AXA holders to fit my BXA post...




Cutting dovetails isn't hard. It's kind of fun to watch even. I don't see any reason you can't open up AXA holders. They wouldn't be as ridgid, but probably good enough for a lot of work. At that point though, you're not that far away from just making a batch of holders.


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## jwmelvin (Mar 23, 2021)

Thanks for the encouragement, both of you. I’ll have to start looking for a dovetail cutter.


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