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Old 10" Howa from 86 Mazak QT20 rebuilt by Michael Thomas what to replace it with


Mar 23, 2016
Howdy all!

Eric here from Colorado. First Post.

I purchased the Mazak QT 20 that Michael Thomas rebuilt. I have lurked on this forum for ages and there are some rock stars here for sure!
There is a broken grease zerk in one of the master Jaws so I took it all apart -- thanks to this forum and a call to My buddy Mike.

No one I know has any experience with powered chucks. This is a Howa H027M 10R-431 chuck.
I am more of an R&D and prototype "Shop" I have no idea what I will be making or when. (This is my retirement plan) I have been slowly collecting Mikes used machines when he upgrades so I can make stuff and learn more about machining and mechanical design. I have been with Advanced Energy for 28 years in various electronics engineering positions, field service engineer for solar, and when they sold off the solar sector I switched careers to Mechanical design. I have been designing all kinds of crazy high power RF stuff for the semiconductor business now for about 6 years in Solidworks. It is great because when they need something quick, and our machine shop is booked I can bring it home and make the parts.

I am finally digging back into this machine after some years of only using it as a manual lathe for little stuff. I have a few things piling up now that will require me to re-acquaint myself with programming. I did it before so I am not too worried about that. What I am trying to do is make this machine do I can do about anything on it. I have some steel soft jaws Mike had and made some ER32 adapters I can chuck into it. All fine and dandy with a one setup small job.

Is it possible to have hydraulic chuck with stepped hard jaws that are repeatable with low runout? Then take them off, throw in some properly cut soft jaws to chuck up an ER32 collet adapter and be right back in business with low runout?
I do not even see a way to adjust the chuck I have now for runout if I were to grab a set of the steel stepped jaws. I would guess I would have to somehow get a grinder in there and once installed true them up. But when I switch them in and out as long as I keep the same chuck on the same jaw is it repeatable?

Or is all this a pipe dream?

Mike had thought this old Howa chuck was pretty worn out. I don't even know how to tell if it is worn out because I do not know what to expect from a powered chuck like this.

If I were to buy a new 10" chuck what should I be looking at? Only quote I got so far was from Huron Machine for an Atlas chuck 2.5" through hole (I want to keep that capability) one set of their Collet jaws that accept 1026 SERIES PADS and one set of 2.5" smooth pads, one set of steel 3 step hard steel jaws and one set of steel soft jaws. $5,550. I can make a new ER32 Collet chuck to fit into the 2.5" collet pads. Then later as I actually get some paying jobs, I can get more Pad sizes.

I could also just get another HOWA replacement for $3,600 I think he said. It would be great if the 4 sets of soft Jaws I have now would work on the Atlas as it has the same 1.5mm x60deg serrations but the sales guy did not know if they would work because the Howas are larger. But I figured if the serrations just hung over what was on the Atlas what is the big deal?
I know nothing about what is a good 10" power chuck. It is not going to be used in any type of production environment. lots of small batch runs of all kinds of different stuff that I don't even know about yet. So I am trying to be prepared to be as flexible as I can be.

Ohh, and is this the correct place to check for spindle Bearing runout? I think I need to stone it off a little to remove some burrs. I get a little indicator jump 2 times each rev.

I hope the whole power chuck thing is not just a Chevy vs Ford kind of deal but I suspect it may be.

Thanks for all you have already taught me and not known!
Eric from Colorado


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Mar 23, 2016
Well, it is cleaned up and put back together. 80ft lbs on the 3 M12 screws for the back plate. Runout ended up surprising me Mike did a good job cleaning and packing them bearings all them years ago. Looks like maybe 2 or 3 tenths.
I am not looking forward to trying to thread this heavy sucker back onto the draw tube. That strap will help some. But man it is gonna be hard to feel if it is cross threaded or not before any damage is done. Draw Tube Threads OD are 74.8mm with 2mm thread spacing.


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Mar 23, 2016
I ended up installing the chuck today. M10 Eyebolt arrived so I could redneck wench it in place and turn the spindle to thread it onto draw tube. Then I realized I did not know how far to thread the chuck onto drawtube before bolting it down.
I ended up threading it on until the Spindle Key bolt touched the chuck ring then backed it off one turn. It all works but now I am wondering how much travel I should have. I did not measure it before like a smart person would have.
Master Jaws are flush with outside of Chuck when open and when actuated they move 3mm. So they are 3mm inside the outer surface of the chuck. Is that the normal travel on one of these old Howa H027M10 chucks? If it is not moving enough I would guess I need to unbolt it, pop it off the taper and back off the draw tube one or more turns. Is that correct or am I already good to go? There are no fancy markings on the jaws and chuck face to show travel limit and full clamp and full unclamp expected positions.


Sep 18, 2006
Abingdon, VA
The drawtube pulls back to clamp. So if your chuck travel is maxing out when open, then you gain more overall chuck travel by shortening the drawtube---gaining travel in the closing direction. Just don't shorten the drawtube (or screw the tube/nut/chuck on farther) so much that you lose maximum travel in the open (drawtube push) direction.

3mm (.120") may be a bit short for a 10" chuck jaw travel. You can look closely at the master jaws and chuck body, usually determining the limits of travel by subtle wear marks.

I would screw the chuck on another turn or two. As long as your chuck fully opens, you can screw it on as far as possible.

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Mar 23, 2016
Thanks cnctoolcat! I will look at the wear marks. It is interesting learning about how these hydraulic chucks work. Its cleaned and lubed. Going to check the machine level when I can borrow a machinist level this week. I think this thing is so damn ridgid it probably wont much care but worth doing right.

I do not see any place on the casting that looks like a datum I could level off of so I am guessing I will just have to go right to the Z axis Rails in the back. Or is there a better place to place the level?



Mar 23, 2016
After adjusting and actuating it a few times... I got the travel of each jaw to be 4.5mm (.177")
I realized that earlier, when the Jaws were only moving 3mm, the actuator inside the chuck was hitting in the front and topping out or bottoming out..I guess that is a point of perspective. So 2 turns, tighten bolts, actuate a few times, Pop it back off ring, 2 more turns, rinse and repeat until I went too far (I think) went to the point that the plunger was about 1/4" away from the front when opening and I was not gaining any more travel. So I loosened it up one more turn and the actuator is not bottoming out on the open stroke. topping out? Now the actuator looks like it is bottoming out on the open stroke but it is just in the grease, I could leave a strip of .001" shim stock in there when I open it and I could pull it out with no effort. Before, it was getting pinched in there solid on the open stroke. So, Max travel is 4.5mm on this older Howa in the Mazak. I guess it is time to get the wrench out and get them bolts to 185 FT.LBS.

Evidently it is time to buy a Starrett 98-6 level. No one seems to have one to borrow around here. dang-nabbit. The .0002"/10" I have is about worthless for leveling this machine. sneeze and the bubble heads off the scale.