PM-833VT boring trouble

[Tammy63]

I got a PM boring head with my PM-833VT and when I try to bore a hole I get a lot of movement on the 833.

The bit on the left is a PM bit and the one on the right is one I got off ebay from someone selling off a shop.
The PM bits seem to be the worst and the movement has been bed enough that the small one broke.

First video is it just sitting in the hole and not me pushing down on it..

In this video I moved the indicator to the spindle and you can see how much movement I get as I push down and drive it into the hole.

Speed doesn't really matter to how much it moves. The bits I got off ebay are smaller and work better but with a 10 thou cut it will still move 3 thou.

I get similar movement if I use a center drill even with all the gibs locked.

Being new to all this I have to ask what am I doing wrong and how can I fix this? Or is it the mill? If so how can I fix it..

Thanks..

 

[rabler]

There could be a lot going on, but first step is you need to actually grind those boring bars with an appropriate edge (rake and clearance angles), and then make sure they are clocked right. It looks like they are brazed carbide, so you'll need diamond hones or similar.

 

[davidpbest]

Looks to me like a head rigidity issue - probably because the head isn’t locked to the column or sloppy head/column gibs. Without a power feed on the quill, the 833 is not an ideal boring platform - you are forced to hand feed the quill or power feed the head.

 

[Tammy63]

Everything was locked but the quill and I was hand feeding it but I can power feed so I will give that a try and see if it helps.
Thanks

 

[j-becker]

Looks like you identified the problem already: Your spindle moves too much without any load applied. You now need to figure out the cause of the movement. David already pointed out a few potential issues. I am hand feeding to bore on my 833TV and while not very convenient it works fine. I don't think power feeding will make a difference with the amount of movement you are experiencing.

 

[Jason812]

I've had the same issue. Best thing I've done was get an inserted bar and take light cuts. I got replacement gibs and it's still an issue. There's just too much weight up top I believe to be as rigid as one would expect. I've used knee mils and big cnc so my expectations were skewed and I'm learning to deal. I want to spring or gas strut load the quill to take the backlash out of hand feeding.

Last part I bored was a 2" hole in 1.5" thick A514. Wasn't ideal and asking a lot from the 833T, but .05 at a time got it done. I discovered the roll pin on my draw bar was broken. Second part was better after I fixed the draw bar. One day I might get froggy and make a one piece draw bar.

 

[Tammy63]

I went crazy trying to find what was going on with this mill if I pushed on any part of it it would move around 5 thou or more in all directions with all gibs locked. I adjusted all of the gibs to see if that would help but it didn't. I checked the 3 nuts for the head and still got the same thing. I checked the 4 base mounting bolts and they were not tighten as much as I could have because the base that came with it was not made really strong.
I started to tighten the back left one and the dial indicator moved about a thousand so I tighten them all up as much as I felt they would take.

I hand feed this and I took a 10thou cut and then a 20 then 40 and then a 50 thou cut.
I didn't get any real movement and running it at just under 200 rpms I cut it 11 thou from the outside of the wall without breaking through it.

I think I can live with it if it stays the same.

If I push on the head now I only get about 1thou movement. I also was able to drill into hard steel with a better center drill and if I didn't push too hard it didn't move like it did.

Thanks for the help

 

[Tammy63]

Well I was not home with this mill and this problem I'm having with it and I was going to call PM but I didn't have time to do it and I just got a job to fix a rear hub off a TM 250. Bearing went and cut into the hub and I need to bore it out and press a sleeve into it and it needs to fit perfectly but not with my PM-833VT.

I pulled 1 of the 4 column bolts out and checked to see how well made they are and after checking all 4 not 1 was the same cut wit the biggest @0.609 most 5/8 thread should be about 0.615 + so I ordered some SS bolts from McMaster and some shims.

I needed to lift the front 4 thou and I didn't reuse the lockwashers just to clarify if they let the column move or not. I now get no movement when drilling and I ran the boring head in pretty hard @120 rpms with a 20 thou cut and ir was rock solid.

The SS bolts all measured in at .0618 and didn't move around in the threads like the ones that came with the mill leaving me to believe that the threads in the base are good and the bolts lock washers bondo and paint was the problem.

At this point I'm happy with this mill but I really need a Y axis power feed I watch video of you guys running the wheels on your mills like they are supper easy and I have a hard time with mine if I need to do them like you all do..

Good thing I have a lathe and a mill to make something that will work...

I would like to say thank you to all of you skilled guys out there on this site and YouTube because without your knowledge us newbie would not be able to shine as bright as we do...

 

[Jason812]

For fun I pulled one of the bolts and the major was smaller than a 5/8-11 grade 8 bolt I had. I now have 4 new grade 8 bolts and lock washers to install but haven't got to it yet. One thing I noticed was the radius on the column is causing the washer to not set flush and will need some clearance to get a good clamp. Also, the factory lock washers were pretty much deformed to just flat washers. I'm looking forward to see if this helps.

 

[Tammy63]

For fun I pulled one of the bolts and the major was smaller than a 5/8-11 grade 8 bolt I had. I now have 4 new grade 8 bolts and lock washers to install but haven't got to it yet. One thing I noticed was the radius on the column is causing the washer to not set flush and will need some clearance to get a good clamp. Also, the factory lock washers were pretty much deformed to just flat washers. I'm looking forward to see if this helps.

I did not use lock washers because of the clearance...