Recommendations for ATC spindle

[nor2020]

Hi,

I bought a second hand CNC converted Grizzly G0704 and I am trying to do some upgrades on it. First on my list is to build a power drawbar and then an auto tool changer. My question is, are there special spindles for power drawbars? I have attached photos of the spindle (I believe this is the stock spindle that came with mill) currently in the mill. I have to use a wrench to loosen the square head on the top. From what I have seen on the internet, the spindle itself should have some sort of drawbar mechanism that can be pressed down by an air cylinder, I don't know what I have right now. Are all spindles capable of this mechanism or are there special spindles for it?

If my current spindle is not suitable for the power drawbar upgrade, can someone recommend one for a G0704 that uses 110V? Thanks.

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[joeavaerage]

Hi,
if I'm not mistaken Grizzly's have an R8 tapered tool holder, similar (indentical) to that used in Bridgeports.

R8 tapers require very considerable tension to hold them such the that machining torque does not cause the taper to slip.
They also often require a considerable jolt to have them release if you wish to change them. I do not think, and to my knowledge,
no-one has made a successful ATC out of an R8 taper.

Toolholder tapers that are suitable for ATC's tend to have a much steeper taper, often with drive dogs to transmit the machining torque.
There are a number of sizes, in smaller machines such as your an ISO20 is probably right. BT30, ISO30 are very common in slightly
larger machines and BT40, ISO 40 are common in large machines. I have attached a pic of an ISO20 tooholder.

My suggestion would be to change the spindle and bearings to one that accepts ISO20 (or ISO30 or BT30) toolholders.

This is an example of the sort of thing I mean:

https://www.ebay.com/itm/BT30-Taper-...q79gfZA44Yd6EA

Note that this unit has a through hole that would be attached to the ATC power draw bar cylinder. You would use the same motor that you already have.

Craig

[nor2020]

Hi Craig,
Yes, it does look like from my G0704 that it has an R8 collet when I loosened the tool holder. I did some more research and found that some people on youtube along with other companies selling power drawbar kits for the G0704 have said that no modifications to the mill is required and that the kit only needs to be installed. I have not done the conversion myself but after looking at a parts diagram of the mill, there is a drawbar in the grizzly head spindle, so would it be safe to say that the current stock spindle is sufficient and only requires an air cylinder and the Beleville washer mechanism to push down on the drawbar to make it work as a power drawbar modification?

[joeavaerage]

Hi,
that is not my experience with R8 tapers, but then I have fewer than 500 hours experience on a Bridgeport clone, so if there is a kit
then research that.

Craig