Mill slot (PM935) vs vise keys (Kurt)

[Clock work]

Greetings...

I'm setting up my 935 mill and when I went to install the registration keys on the Kurt D688, the keys did not want to install in the middle slot during a test fit. The three slots are of different widths... the key fits the two outside slots and the one toward the base is a tighter fit than the one toward the operator. The middle is a no go. Neither the slot or the key measures on the money and the relationship is reversed.... too tight at the slot (1's of thousandths), too wide at the key (1's of thousandths).

What's normal/cultural best practices? stone the key? Open up the slot... it IS mounted on a mill. I like the fore/aft balance of the vise mounted in the middle. Thanks.

 

[Bob Korves]

Leave the table slots alone beyond carefully cleaning and deburring them. Make your own t-nuts if necessary and get the fit you want. Making t-nuts is a pretty simple job, and you can make them to fir YOUR machine, not the 90th percentile or "within tolerance." Carefully round and deburr all exposed edges and corners so they do not scratch and gouge your mill table, and do not let fasteners protrude from them. I prefer t-nuts made of mild steel. Stop tapping before breaking through the bottom of the t-nut or purposefully distort the last thread or two to keep the bolts from bottoming in the t-slots.

 

[benmychree]

Since Bob is a bit off topic with discussion of T nuts, I'll go one further and say that I do not use T nuts and bolts or studs with nuts to hold vises or other accessories down on the mill table, but I use T bolts, sometimes bought, sometimes turned and threaded square stock; with these, one can use collared nuts, or heavy hex nuts with a separate (thick) washer; they are much more convenient to use than Y nut with separate stud or bolt.
Sometimes, I like to use T nuts that are tapped all the way through, especially in a setup with multiple parts being machined; tighten the stud against the bottom of the T slot and the setup stays put, I also use springs on the stud between the machine table and the strap clamps; this keeps the clamp from falling when changing the parts being worked on, the clamp can just be swung to one side.
I agree with Bob in that you should just deburr the slot, then fit the portion of the key that engages the table slot so that it will fit snugly in the slot. I should talk? My Fray vertical mill still does not have keys to fit the Kurt vise to the table slots, I just indicate it each time I remove and reinstall it; I'll get around to it someday --- it has only been this way for about six years now, no need to rush into these things --------

 

[mksj]

The keys give you an approximation, not the final word on setting the registration of the vise. I mill the registration keys to have a few thousandth wiggle room in the table slot, they help in getting the vise into position and allowing for minor adjustment. I then indicate off the face of a jaw with the vise mounting bolts lightly tightened and tap the vise into alignment, then tighten and recheck alignment. I use threaded T nuts and flange bolts, also hardened grade 8 extra thick washers under the head of the flange bolt head. Never had an issue with the vise moving and alignment takes a few minutes, muche easier with the vise registration keys, but you still need to indicate the vise if you are doing close tolerance work.

 

[Dabbler]

This has come up a couple of times before, but without the T slot width difference.

My first mill was an 8 X 30 but it had unusual T slots. The bottom of the T was configured for a normal 1/2" T nut however the slot itself was .490 +/- .002 for every T slot. I like standards and the closest standard was the 1/2 T slot holdown kit. So I carefully milled all the slots to .510 which allowed the use of a 1/2" kit.

If by careful measurement of the slot and the corresponding bottoms you find they are in any way different and you have the skills, then make them all the same. you will be thankful for the next 20 years. But only if they truly need it!

On the second point - I have a tool and diemaker friend that never uses a rotation base on his Kurt, and has installed custom keys that have a tight fit to each of his T slots. He spent a week to make sure his vise located within a few tenths of 'tram' in every T slot, along the entire usable length. He loves it. Tom Lipton of OXTOOL (youtube) would hate it. He never wants to drag a hardened key across his table.

My vise has no keys and has a rotating base. I 'tram' it every time it goes back onto the table. A headache and a bother. so there you are. You now know my vote.

I use T nuts and a custom length grade 8 bolts, with home made soft steel washers that are about .185 thick. My bolts use the same 3/4" box end wrench that is used for the drawbar, so I only use one wrench for all. It is a Craftsman dual open ended wrench, 3/4" and 7/8".

 

[Clock work]

Sincerely appreciate everyone's conscientious replies. Thank you. They are helpful both on topic but also in providing a glimpse into the domain knowledge that lies far ahead of me if at all. My "day job" is around technical decision-making risk and the big rule each day is "Don't F up"... which can frequently be achieved actively avoiding irreversible decisions, especially early on. The keys are going back in their little envelope until I'm less ignorant and I know not to hold my breath for that to change So, just bolts for now. In a vise related question can I follow up with... would this be a good place to mount my vise handle? Seems nice and close

 

[mksj]

A few comments. First, you might make your own alignment keys for the vise, not a big deal. Put a little chamfer on the key edges so it slides into the table slots easily. This will give you very close alignment (and the same front to back table positioning) and less fidgeting. I have seen various alignment pins/keys for industrial type setups to hold jigs and vises precisely, but I do not see the need for it in this setting. Let alone milling the table slots. My last mill had metric sized slots (like 12mm) so nothing fit, a real PTA.

I would not mount the vise handle on the vise as in the picture, you will not get full extension of the vise when open and I would not want to drill the sliding surface. Might put the vise handle bracket on the side of the knee instead. I normally do not remove my handle from my vise, I added a ball detent to the handle which keeps it from sliding off. I also mount the Z axis crank handle and headstock wrench off of the Z axis drive stop rail. Many people switch to a vise speed handle, they come in various forms and sizes. I repurposed my vise speed handle to use it on my 5C chuck, I had the Gibraltar below, it was just OK.

 

[Clock work]

Hi MKSJ and thank you sincerely for the great suggestions. I really should solve it as you suggest.. make the keys on the new mill. Really like your other suggestions as well about handles and such. I'm not in love with the stock one really. As far as my idea to mount the holder on the ways of the vise (or whatever that areas is called), it was more a bad joke invoking the know-everything tone of my remark a couple of sentences earlier about irreversible decisions Thank you again and have a fantastic Thanksgiving.