T-nut sizing & milling down too-large T-nuts

I just picked up a Rusnok milling machine and need to get some T-nuts to fit.

The manual and all of the specs literature online says the T-slots are 5/8" nominal, which I don't believe after measuring it and seeing a post by someone else on another forum that said 9/16" nominal. Here are my measurements (just done with a digital caliper held in an awkward way, so figure +/- 0.005")

My measurements don't appear to match anything in the Te-Co catalog, so I'm thinking about buying & cutting down the next size up, which is 0.005" wider than the narrow part of the T-slot and 0.027" wider than the wide part.

So:
-Is there a standard nominal size that is a good fit (i.e. am I way off here)? (I'd rather not spend time making stupid stuff like T-nuts)
-What amount are the dimensions of the nuts supposed to be undersize compared to the slot?
-Are Te-Co nuts hardened?

[/quote]

Which part of 0.625" doesn't equal 5/8"?

I've modified many t-nuts you can use a surface grinder to make them to fit or set them up in the mill and machine them.

JLarsson said:

Which part of 0.625" doesn't equal 5/8"?

Click to expand...

The part where 5/8" nominal T-slots are supposed to be 0.688" wide at the top (like pipe sizes and knockout sizes, nominal does not mean actual measurement...it just means nominal). From the engineer's edge standards reference:




Nominal___________Width of
T-Bolt_____________ Throat A1
Size________________

inch___________inch
0.250___________ 0.282
0.312___________ 0.344
0.375___________ 0.438
0.500___________ 0.562
0.625___________ 0.688
0.750___________ 0.812

In addition, the question of hardened nuts vs non-hardened was recently discussed. You might want to read through this recent thread:
http://www.practicalmachinist.com/vb/general/t-nut-clearance-milling-table-slot-326970/
Lots of good info.

Denis

dgfoster said:

In addition, the question of hardened nuts vs non-hardened was recently discussed. You might want to read through this recent thread:
http://www.practicalmachinist.com/vb/general/t-nut-clearance-milling-table-slot-326970/
Lots of good info.

Denis

Click to expand...

On this note, I took a look at my old Reid Tool catalog. They offer two different lines of Tee nuts and associated hardware. BOTH are described as case hardened. Approach milling with this in mind.

A few factors you should be aware of when dealing with (learning the basics of) T-nut/slots.

Maximum bearing on the shoulders of the nut/table interface is what you want to distribute the clamping forces. Don't bear on sharp edges/radiused corners. Make sure chamfers clear inside corner radii. Don't clamp on chips/swarf. Keep things clean when making a set up.

Check the slots in your table. The 5/8" may be narrowed in areas where the previous weak minded & ham fisted operator over tightened and/or used inappropriate nuts. Run a good sharp file along the walls of the 5/8" slot to locate and remove any 'high spots'.

Also, T-slot nuts are available in 'blind tapped' and 'tapped through' styles. You probably want the 'blind tapped' type to prevent inadvertently driving a stud into the bottom of the slot. I often use 'tapped through' type when using a cap screw, rather than a stud, but take extra care not to bottom out the cap screw.

Commercially made T-slot nuts are case hardened so I recommend that amateurs grind them to fit. Be sure to replace any edge breaks/chamfers that resizing removes.

In your case, the .937" dimension seems to be your only problem. Just buy some nuts with 1" base width and grind them to fit.

Be sure to post back to this thread describing your process, with numerous photos, so the information can be easily found by the next (what's the best word?). . . person.

dgfoster said:

In addition, the question of hardened nuts vs non-hardened was recently discussed....

Click to expand...

Actually, I don't have access to a surface grinder while I'm staying on the west coast. So the plan would have to be to anneal the case-hardening out (or at least heat to 6-800°F and slow cool to temper) before milling OR pick up one of those carbide endmills designed for cutting the hard stuff.

Man...the Rusnok is beautifully engineered... but would picking a standard size have killed them?

catalytic said:

Man...the Rusnok is beautifully engineered... but would picking a standard size have killed them?

Click to expand...

When that was made I doubt there was a ''standard size'' of tee slot.

Quick, easy and plenty strong enough tee nut for your app.

From 1.5'' -larger is better, bar (even 12L14 is fine) turn a spigot that clear the tee slot width and below table surface.

Drill and tap the full depth of your tee slot, say a full 7/8'' ........on a machine that size 3/8 will be plenty.

Part / cut off so the flange will clean up to fit the bottom part of your tee i.e. .0.390''

Hack saw / mill / whatever, equally either side of the flange to fit your width i.e. 0.973 -

Knock the burrs off and use.

extropic said:

... Don't bear on sharp edges/radiused corners...

Click to expand...

That doesn't seem to leave many options - or have I missed something?

George

Let's think outside the box. If I understand the problem correctly, the tee-slots are a little undersize compared to standard slots. Well, this is a MILLING machine.... Why not mill out the slots? I am pretty sure I would do that rather than chase around making special tee-nuts now and every time I needed a few more.

Denis

Monster T slot for such a baby mill. Commercial T nuts are way overkill.

Grab a short foot of extruded alloy bar and chomp out a stick to "rattling good fit" in the slot size. Tap to any convnient size making sure the bottom thread is incomplete so you can't drive the stud or bolt right through. I find a flat ended second cut tap leaves a sufficiently incomplete thread if taken down to no more than flush with the bottom face. Just be careful to get the top faces of the T cross bar on the same level so the nut comes up square in the slot and ensure the tapped hole is exactly perpendicular to them. Everything else is in the wind so small variations and slight out of squareness matter not a jot. Best if things are close tho'. Offended aesthetic senses tend to adversely impact the quality of work done.

I've always preferred studs to bolts in Tee nuts. If rolling your own its easy enough to make permanent Tee nut and stud assemblies, especially as you only have one T slot to worry about. There is an argument for using stand-offs, internally threaded at both ends screwed onto short studs in the Tee nuts for all except the shortest stud 'n nut combinations. Stiffer than a simple stud, so adequate clamping is often possible via simple bar on top, and it holds the assembly in place by nipping down onto the top of the table when screwed on. With small work nipping the T nut and stud in place can be a great help in getting stuff tied down. Small items tend be light and easily moved. Often the feature you are clamping on is quite small too so it really helps if at least one part of the clamping arrangment is tied down before you start.

With only one Tee slot you may well find X, Y and V shaped clamps useful. Wedge step blocks seriously get in the way on these small machines. Much better off with stacking spacers and a short jack screw on the clamp bar. Just don't run the end of the jack screw direct on the table. Personally I'd pretty much forget the whole T slot thing and fit a grid of holes plate on top of the table. The aluminium breaddboards from Thor Labs do just fine.

Clive

Just buy a clamping kit for 9/16" T-slots. Travers Tool has them.

HuFlungDung said:

Just buy a clamping kit for 9/16" T-slots. Travers Tool has them.

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9/16 T-nuts are ~0.560 wide at the top and 0.875" wide at the bottom.

This means they would be undersize by 0.065" at the top and 0.098" at the bottom. Is this too much?

catalytic said:

9/16 T-nuts are ~0.560 wide at the top and 0.875" wide at the bottom.

This means they would be undersize by 0.065" at the top and 0.098" at the bottom. Is this too much?

Click to expand...

Perfect!

When you get a bunch of chips down in there, you still want to be able to slide them out without undue force, rather just a bit of rattling and wiggling and they come free and move.

The precision width of the T slot is meant for keying fixtures to the table accurately.

Just a piece of flat stock to fit the bottom of the T slot.

HuFlungDung said:

Perfect!

When you get a bunch of chips down in there, you still want to be able to slide them out without undue force, rather just a bit of rattling and wiggling and they come free and move.

The precision width of the T slot is meant for keying fixtures to the table accurately.

Click to expand...

Sounds good -- thanks!!
I've been machining for a number of years & finished formal training a few years ago, but this is the first time I've had to order my own tooling... it's shocking how many details I didn't know about the stuff I'm used to using.

rustytool said:

View attachment 184271View attachment 184272Just a piece of flat stock to fit the bottom of the T slot.

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Why didn't I think of that. It's not like I'm going to be needing enough force on this baby Rusnok to actually use the extra threads in a full-height T-nut. I'm sure the standard warning about through-threaded holes and jacking up the bar/breaking the T-slots applies.

For pity sake, you are not the first one who needs an odd size T-slot nut. They make them in many, many sizes. I purchased a "standard" clamp set for my mill and the nuts did not fit the table. So I bought new nuts. No problem and no grinding. Here are eight from MSC that appear to fit your slots. If you do not like any of these, just back up in the search and use your own numbers.

T-Slot Nuts | MSCDirect.com

Georgineer said:

That doesn't seem to leave many options - or have I missed something?

George

Click to expand...

Planar surfaces.

I've had the same problem with my rusnok. Soon as I get my maho working I've got to make a proper set rather than the hand ground down set I've been using. They sure are nice mills though. Only thing I don't like is the motor should probably be a tad bigger. It heats up a lot after lots of milling. I got the mill from a old guy and it was basically new except for it having a broken gib (bought a new one from EM) and 2 marks on the table. Cleaned all the rust off of it and it's been serving me well.