[4]

learned a lesson about RF30 style mill

[3]
[10] Like what you see?
Click here to donate to this forum and upgrade your account!

Investigator

Active Member
Registered
Joined
Jun 8, 2016
Messages
297
I've heard about the problem of holding zero on a round column mill when raising or lowering the head. I know about it and have been able to work around it so far with no problems. This weekend while trying to mill out pocket in a piece of aluminum, I noticed my slot was moving. First cut was ok, second cut was offset about 30 thou. moving back to my starting point, my DRO's were off by over .250"

Long story short, the head was not tight enough and was turning as the table moved.

Round columns have pitfalls, and I found one I hadn't heard about before. The fix was to properly tighten the head and take lighter cuts. To be honest, I was taking about a .100" deep cut in 7075 with a 3/8 end mill. I was just hogging it out, but it was a bit ambitious.

Tighten the column and take realistic depth of cuts.
 

Investigator

Active Member
Registered
Joined
Jun 8, 2016
Messages
297
I have heard of using fine thread bolts as replacements, these look like the same threads. What makes these work better?
 

pontiac428

Mo-Max
Registered
Joined
Apr 23, 2018
Messages
572
I guess it's hard to see in the photo, but the new studs are 5/8-11 up from 1/2" stock. The new studs have a much larger clamping area, and the cup washer tolerates misalignment from the Taiwanese casting. Plus, it's still a direct fit for the nut recesses in the left side of the column clamp. It's about $25 worth of hardware and it fixed my issues. I can use a normal amount of torque, and now my mill head stays put under load.
 

martik777

Active User
Registered
Joined
Apr 19, 2011
Messages
556
I think some head to column fits are tighter IMG_20190624_121320879.jpgthan others. I just hand tighten mine with a lever I made - no issues.
 

mikey

Active User
H-M Platinum Supporter ($50)
Joined
Dec 20, 2012
Messages
5,548
Another thing to be aware of is that when you tighten the two bolts the head moves by a few thou. Mine moves 0.0025" as the bolts are tightened and the head straightens up on the round column, and it doesn't matter if you tighten the upper or lower bolt first. I tighten my bolts to 35 lb/ft of torque to keep things solid and consistent. I have not had the head move even once so I guess it works.
 

Investigator

Active Member
Registered
Joined
Jun 8, 2016
Messages
297
Mikey I was hoping you jump in. I tighten mine "as tight as I can" with a 3/8 ratchet, no idea what foot pounds.

I never thought about it moving while you tighten it, it never came up. I always tighten and then re-indicate as needed.

Pontiac, I am pretty sure mine are already 5/8-11. Somewhere I seem to remember reading that it was easier to tighten up, as in would tighten up a bit easier with fine thread bolts. That's why I say I have 5/8 now, I went looking for fine threaded bolts that size. Somehow I made a mistake and the bolts I bought were about an inch short and didn't extend past the other side, I couldn't get a nut on them. I never revisited that.
 

pontiac428

Mo-Max
Registered
Joined
Apr 23, 2018
Messages
572
I may have misspoke when I said the stock bolts were 1/2", they may have been 9/16".

My only argument about going fine thread is that these are pinch bolts that are routinely handled by the operator, similar to a Kipp lever. If the threads are coarse, the lever throw is short, and if the threads are fine the throw becomes longer. With improved contact under the bolt heads, even with the coarse thread I get good holding power under modest torque (a humane pull on a 10" breaker bar does it). All I can really say about it at the end of the day is I had problems with the head slipping about the column, and now I don't, and I'm not doing anything else differently.
 

mikey

Active User
H-M Platinum Supporter ($50)
Joined
Dec 20, 2012
Messages
5,548
We're better off with coarse threads; they handle heavy loads better than fine threads.

Scott, I wouldn't have thought to check head movement when tightening the head bolts either but I'm in the process of evaluating the True Line 8 and this is one of the things I had to contend with. More on this eventually but the torque on the head bolts does make a difference in how accurately the head aligns, or realigns. I think if you torque the bolts consistently and with adequate torque then you should be good. The question is what is adequate. I found that 35# is adequate; below that and the readings get more inconsistent. Just a FYI.
 

darkzero

Global Moderator
Staff member
H-M Supporter - Gold Member ($25)
Joined
Nov 27, 2012
Messages
3,818
If the machine is Taiwanese it's very possible that the bolts are imperial. Many Taiwanese metal working machines are made with imperial fastners but of course not all. For Taiwanese mills & bandsaws I have seen them more commonly with imperial fastners than metric.
 

mickri

Brass
Registered
Joined
Oct 31, 2016
Messages
643
When I first got my mill/drill I read tales of woe all over the internet about the head going out of alignment when you needed to change tooling. I looked at all kinds of contraptions that people came up with to solve the problem. Then I happen across a video where it was suggested to figure out all of the tooling you would need to use for a particular project and set the head at a height where you didn't need to move the head to change tooling. I have followed that suggestion and so far I have not had to move the head while doing a project. I can't even remember when was the last time I moved the head on my mill/drill. One thing that really helps is using ER32 collets to hold the tooling. ER32 collets are very flexible when it comes to changing tooling.

Back to the issue of tightening the bolts. My mill/drill has 3 bolts. I tighten the middle bolt first then the bottom bolt and finally the top bolt. I do this in stages just like I do when tightening head bolts on an engine.
 

MarkM

Active Member
Registered
Joined
Apr 23, 2017
Messages
495
You will greatly benefit with the use of fine threads. A much stronger thread with more surface contact. More Torque is applied with the same preload and also the fact fine threads have less chance of loosening due to vibration because of the greater surface contact.
As far as having a shorter throw. Does it really matter between being tight and loose?
 

Cadillac STS

Active User
H-M Platinum Supporter ($50)
Joined
Jul 20, 2012
Messages
750
When I first got my mill/drill I read tales of woe all over the internet about the head going out of alignment when you needed to change tooling. I looked at all kinds of contraptions that people came up with to solve the problem. Then I happen across a video where it was suggested to figure out all of the tooling you would need to use for a particular project and set the head at a height where you didn't need to move the head to change tooling. I have followed that suggestion and so far I have not had to move the head while doing a project. I can't even remember when was the last time I moved the head on my mill/drill. One thing that really helps is using ER32 collets to hold the tooling. ER32 collets are very flexible when it comes to changing tooling.

Back to the issue of tightening the bolts. My mill/drill has 3 bolts. I tighten the middle bolt first then the bottom bolt and finally the top bolt. I do this in stages just like I do when tightening head bolts on an engine.
Often times the tool that needs the change in height is the drill bit. So having a set of stubby drill bits can solve that problem and not need to change height when you may have had no choice with the long bit.
 

mickri

Brass
Registered
Joined
Oct 31, 2016
Messages
643
If you are using a drill chuck then drill length can be a real problem. On the other hand the ER32/R8 adapter is hollow so you can slip those long drills up inside the adapter when changing drills. This is one of the reasons why I went with ER32 collets when I was setting up my mill/drill. I have never used a drill chuck on the mill/drill.
 
[5] [7]
Top