Help with milling issue

[redhouseluv]

I've started this as a new thread and as its a general issue not specific to the build I'm working on. I'm a bit puzzled and frustrated and I've ground to a halt due to the following and looking for some help please.

I'm making the split bearing in the picture and noticed a discrepancy in the slot I had cut.

- 0.010" difference over 0.982" - cutting along y-axis
- I wondered if the mill jolting I had earlier this week created a the problem so trammed the y-axis
- 0.0005" difference on the gauges across 130mm (see pic) so it can't be that?

What could be causing the problem?

- I used a mini level in the picture and needed 0.0065" of packing underneath one side to get it level. This to me indicates the entire mill is not level, but is that relevant if the tramming gauges indicate what they do?
- Could it be the vice I'm using?

I need to understand what is causing this and correct it before doing anything else!! 

[Jasonb]

To me that is a glorified drill vice and you may well be getting jaw lift.

Put a similar size piece of stock in the vice and rest the dti on top of it and see what readings you get on the back and front as you tighten the vice.

[redhouseluv]

Ha - I think you are right!

I've just this second taken some new measurments across the vice jaws; I had the work piece sitting on the edges and not on parallels and look at the difference. That according to my mm to inches conversion is 0.0035" - 0.004" across such a small gap. Also the difference changes up/down depending on where you measure along the x-axis

I need a new vice - any suggestions?

[crueby]

The screwless vise type is what I  use. Rather than a horizontal screw at the back of the jaw, there is a screw running diagonally down through the jaw to a cross pin that engages a series of slots underneath. They come in a variety of sizes and are not too expensive.  There are also other types of milling vises, but I don't  have experience with them  so I will  let others speak to them.

[redhouseluv]

Have you a picture of one please?

I just realised I have this one, which was given to me some time ago. It looks and feels substantially better engineered and weighs double the other one. I'm not sure in terms of accuracy, but as Jason mentioned, I'm sure a piece of scrap will determine that.

[redhouseluv]

The screwless vise type is what I  use. Rather than a horizontal screw at the back of the jaw, there is a screw running diagonally down through the jaw to a cross pin that engages a series of slots underneath. They come in a variety of sizes and are not too expensive.  There are also other types of milling vises, but I don't  have experience with them  so I will  let others speak to them.

I know which ones you mean, I have one, maybe I should use it for work like these bearings, rather than the other type.

[Jasonb]

We discussed the issues with teh "screwless type in the other thread.

The Warco one would not be so bad if you mad used parallels and knocked the work down after tightening the jaws.

Have you tried that old Abwood one?

On the CNC and for some manual work I use one of teh ARC versatiles in 80mm width (also have the 100) which seems to work well and jaw lift is not really measurable. https://www.arceurotrade.co.uk/Catalogue/Workholding/Machine-Vices/ARC-Versatile-Milling-Vices-with-swivel-base

Main one I use on the Manual mill is the Vertex K4 which has a small amount of lift but nothing a copper hammer can't sort out. Mine came from Chronos but I don't think they do them now but they are about on the net.

Couple of measurements of liftI took comparing a 90mm screwless and the two above

[redhouseluv]

I haven't tried the Abwood one, but will do; the only issue with it is that it doesn't open very wide for larger work. I'll give it a go before spending any further $s. Those Arc ones look good as do the Vertex and aren't too crazily priced. I bought quite of bit of cheapo stuff when I first started out and gradually over time have had to replace them with better quality stuff......not an unusual story I'm guessing! 

BTW switching to the precision vice sorted out the issue straight away; I had to complete a few passes to bring the work back to an even keel

[uuu]

I have vices that claim to stop jaw lifting, but don't really work.  The Abwood design is good - the moving jaw is supported over a decent length - there are gibs you can adjust to keep things tight - the thrust from the screw is up where the jaw is, not below it.

Wilf

[john mills]

The abwood is a milling vice i have used them 6""ones but they were worn out  .replaced one i used with a hydraulic   8"   weighed 95 kg used that for years.
but that was for heavy milling and for mostly hot work die steels.
they still need the material to be knocked down to be in the right position i used a lump of copper 1 1/4"dia 6" long
john

[Chipswitheverything]

  For work within its scope of size the Abwood vice should be excellent : I have a similar one that I bought new, very many years ago, and I can rely on it for precision.
A few years back, I inherited from another model engineer a 4" jaw far Eastern manufacture machine vice of the general format of your vice.  Quite substantially made. When I checked it over, a lot was wrong with it!
 So I treated it a bit like a set of castings, and remachined and re-fitted a lot of surfaces, re did the jaw seatings which were all over the place. Re machined the moving jaw guideways and the gibs that hold down the jaw, so the lifting tendency has been eliminated.  Filed and scraped the base of it flat, and re-did the tongue and groove for the ( new) tabs to fit snugly into the milling table slots.
 After this, I have found it to be a good and useful vice!, no prettier appearance wise, but I can rely on it for holding with decent accuracy.  So at some time it might be worth seeing if a 'fluence could be worked on your vice ...  Dave

[Charles Lamont]

As I usually do at about this point in a discussion involving milling vice jaw lift, I will throw in the use of "pull-downs" for getting accurate parallelism. These are strips of material with bevelled edges used between jaw and job to exert a downward force on the job. It may look a precarious arrangement, and it can be a bit of a pain to set up, but it works well. I often use just one on the moving jaw side. The sketch show two types. I prefer the one with the V on one side as being easier to set up.

[Jasonb]

Charles, How are those with the softer material like aluminium or in this case GM/Bronze? Is there a chance of the narrow contact area marking the work?

[Charles Lamont]

Yes they will mark a softer workpiece, but getting the two largest faces parallel is often the first task, before finishing the sides.

[dieselpilot]

At that angle the reading on the dial indicator must be corrected for cosine error. The stylus should be parallel to the surface for that model, if the reading is to be used directly.