[David_Nolan]

I have a mini mill designed for MT3 taper, I've been trying to figure out if the slot my MT3 tools go into is tapered internally or is just a straight hole (It's hard to tell). What's the standard, can morse tapers mate with normal holes wihout losing concentricity. I wondering because I'm planning on designing a spindle at some point and having it machined in a machine shop. I'm thinking it would be nice if I didn't have to bother with the internal taper but concentricity is paramount. So do I need to design an internal taper?

[switch2472]

Yes, you must use a mating taper.

Milling machines normally would not use a self-locking taper like the Morse taper, if you are having a new spindle made for a mill, go with an R8 taper for manual tools, or an NMTB-standard taper for any of the automatic tool changer systems.

[joeavaerage]

Hi,
if you use Morse tapered tool holders then you will need a matching internal taper in the spindle. That's how the power is transmitted.

If you use BT40 toolholders, then you need a BT40 internal taper......if you use HSK63 toolholders then you need an internal HSK63 taper....etc.

As switch2472 has suggested R8 is good for a manual toolchange machine but one of the BTnn, CATnn, ISOnn tapers are required for auto toolchange.
BT30 is good up to several horse power and BT40 for more than that. HSK tapers are great for highspeed spindles but the toolholders are quite pricey, whereas the BTnn,
CATnn, and ISOnn toolholders are common and well supported, with fair to good quality toolholders fairly cheaply.

Craig

[dazp1976]

I swapped my mini mills (2spd geared) spindle shaft to a R8 one when I converted to a belt drive.
Found it to be much better.

Yes they are tapered internally.

[David_Nolan]

I'm having trouble, because I can't farbricate this myself so I'm using a machine shop, they're going to fleece me for high tolerances so what I'm wondering is how do I avoid that. Do R8 Tapers also need matching mating tapers? If so what are the tolerances... I found a figure in machinery handbook, it was 0.002" per foot (For morse tapers). I don't understand what it means by that figure. I mean I understand what it means by a 2 thou tolerance but not the per foot part and where do I take those measurements?

[pippin88]

If you don't understand tapers you have a lot of learning before you can build a spindle.

Why do you need a custom spindle?

Buy a spindle from China

[joeavaerage]

Hi,

Do R8 Tapers also need matching mating tapers? If so what are the tolerances...

That's a resounding YES. All tapered toolholders require a matching internal taper with tolerances measured in the 'tenths of thousandths of an inch'.
Making a internal taper is no mean feat.

If you insist on making your own spindle consider this:

https://www.ebay.com/itm/CNC-Milling...Cclp%3A2334524

Because the shank is cylindrical you can use 'ordinary' angular contact bearings....but note that it will be strictly manual tool change.

Craig