Putting a T-slot in a curved edge.

[Bogstandard]

Has anyone any pointers about putting a T-slot around a curved edge?

If not, can anyone forsee any major problems? I just can't seem to get my head around it, and a quick push in the general direction would help.

I am thinking of using a small T-slot cutter on the mill, but if this is a non starter, maybe cutting around the edge on the lathe, using a ground up tool.

Any help would be much appreciated.

John

 

[DickDastardly40]

What sizes and what material are you talking about John?

If I understand correctly what you want to do and it is a half profile of a T slot on the full periphery of a circle, I'd chuck on the lathe and use a combination of knife and parting tools to get the shape required.

If not on the edge, how about trepan the slot and then use a internal recessing tool to open out the - of the T cutting the outer normally and the inner with the chuck running backwards and the tool behind.

Am I clear? Prolly not.

Al

 

[Bogstandard]

Al,

I am after putting a full T-slot on the edge of a curve in material about 3/4" wide, so the slot would be about 1/4" and the T would be about 1/2" wide. I have the required milling T-slot cutter, I was wondering if it would cut on a curve or not. A curved T-nut would then be used. Imagine having your milling table bent in a curve from end to end, the T-slots would be curved.

John

 

[SandyC]

I am very surprised you, of all people, even asked the question John....... SAVE your T-Slot cutter for a straight job, they are to expensive to junk.

Any attempt to cut a curved slot with one of these cutters will end in disaster...unless the radius is about 300yards......the leading LOWER, cutting point will dig in to the bottom of the cut, whilst the trailing UPPER points will dig in to the top of the already cut portion of the slot....result....the cutter will jamb, and probably shatter.... even if it did not, the slot would certainly be very rough and almost unuesable. They just don't take to being twisted in the slot.

Better to do it on the lathe with a parting/grooving tool for the main slot, then right and left hand form tools for the tee sections.

I would hate for you to have an accident John, so go the right way my friend.

Best regards.

Sandy. ;D

 

[Bogstandard]

As usual Sandy, looking after my back.

The reason I asked was that I have never done it or seen it done, so if it was possible, I would have followed the advice.

The advice you have given was what I was after, so the milling route is now out. Thanks.

I only want a partial arc (about 60 degrees), and thought an interupted cut on the lathe wouldn't be ideal using a slim profile tool.

I think maybe the way to go would be an external T and make the follower a two piece job, so I can machine the internal and external curves on the RT. Or even a two piece plate so when put together they form the T-slot.

Decisions, decisions.

Thanks again

John

 

[shred]

You could do a lolly-shaped slot using a reduced-shank ball cutter in the mill, but I'm not sure how well a ball-ended 't-nut' would work.

 

[Bogstandard]

The problem with using a round hole Shred, is that when pressure is put on to tighten, the ball on the end will act like a wedge and try to force the slot apart.

I could get my friend to EDM the slot on the edge, but it is such a big exercise for so small a project, it isn't worth doing.

I will find my own little way to get it done, eventually.

John

 

[SandyC]

;D

No problem John..... Just don't ask how I found out!!!!!

The 60 degrees certainly puts a different slant on things, and yes, it would be nigh on mind bending trying to do this with a form tool....it would need to be hand driven.

Certainly the split plate would be the easiest method, and probably the most accurate, however, a lot depends on whether you can live with a full face joint at plate mid-section.
E.G. If you needed to add top slots, or some other feature to the plate then the joint may become an issue.

The alternative would be to just machine a half depth segment from the bottom of the plate, in the region of the required T slot and make a matching segment to bolt on place.
In either case both top and bottom sections could then be easily slotted on the RT, at the same setting to get radial the alignment correct, and the T nuts could be inserted before the lower plate/segment is bolted in place.

The point you made about the BALL shaped slot is very valid...... the G H Thomas rotary table used a wedge shaped slot (same problem with tee cutters) and this also created a bell mouth effect, jambing the sliding nuts, if they were tightened too much.

I am sure you will solve it in your own masterful way.

Best regards.

Sandy ;D

 

[Circlip]

If you're going the two part way John, you can cut the double slot in the top plate and use a plain bottom plate fixed from underneath. Regards Ian.

Some confusion here John, Lew and I are on different parts of the curve. Is your tee slot curved like a piece of railway track, or like a hump backed bridge ????

 

[Lew Hartswick]

I think I'd do it with a buildup of 3 parts if I wanted it to be smoothe acting.
...lew...

 

[Bogstandard]

Ian, if it was like a train track, the cutter should work ok. I want mine like a humpty back bridge, and as Sandy was saying, it is the top and bottom of the cutter that causes the problem.

No worries, I will sort it in my usual wierd way.

John

 

[DickDastardly40]

If you get the opportunity could you please post how you do it so we can file it away for future reference.

Regards

Al

 

[mklotz]

This may be a stupid question but would it be possible to put a T-slot in a flat piece, bend it to shape, and then weld/braze it to the parent piece?

 

[Bogstandard]

Marv, as usual, a very good solution to my problem. Lateral thinking again.

Being ali, I would bolt it on thru holes and recesses in the bottom of the slot.
My slip rolls should easily be able to curve it with no distortion to the T. It isn't that critical anyway.

Go to the front of the class.

Thanks, and consider the problem solved.

I love this site, a problem shared is a problem solved.

John

 

[Mcgyver]

as declared, no way its happening with a rotating cutter. I haven't had the pleasure of such an operations and chances are I'll design my way out any curved t slot corners in which i may find myself .......but....Prof Chaddock put on of these on his Quorn and in his book describes making it pretty much as per Sandy's instructions above. grinding up the little L shaped bits will be a pita given all the clearance angles - btw, what are you up to with curved t slots?

 

[Bogstandard]

Mcgyver,

I was looking at making something like a square faced vertical boring bar, but actually with three cutting faces to allow it to cut behind itself to take into account the curvature.

An easy job to do if I could get a grinding fixture made for my surface grinder table that had a T-slot cut into the back of it. Catch 22 methinks.

Sketch attached, but sticky out bit a lot less than shown, only 1/8" protruding, with a 1/4" shank.

Don't know whether it would have worked or not.

John

 

[shred]

The problem with using a round hole Shred, is that when pressure is put on to tighten, the ball on the end will act like a wedge and try to force the slot apart.

I could get my friend to EDM the slot on the edge, but it is such a big exercise for so small a project, it isn't worth doing.

I will find my own little way to get it done, eventually.

John

Yeah, you would have to use a large enough ball, neck and slot that the prying forces were reasonable. I'm liking the other ideas more anyway.

 

[bob ward]

Could you use a T slot cutter if the top of the cutter was shaped to the same radius as the hump back bridge?

 

[Bogstandard]

Bob,

Anything is possible and could work if you had the time and equipment for development.

But I don't want to go into too much detail, as it is experimental, and Marv's suggestions looks to be the easy way around the problem. But what I am trying to achieve is a stop fence, that can be easily and rigidly fixed at one end, and the opposite loose end is always perfectly in line with the centre point of the arc, with no protrusions or adjustments above the top face other than the fence itself.

I can't tell you any more as it might become a viable commercial product. If not it will be recycled. This bit is only a small part of it.

John

 

[ianjkirby]

I have actually cut such a T-slot in the Quorn T&C grinder (in a piece of beautifully machinable cast iron), in exactly the way described by Chaddock, and above by Sandy. It was not at all difficult, and took longer to think about and grind the two L-tools necessary than it did to make the cuts, which worked quite well. As for cutting only a partial slot, well, you're on your own there mate, I'm afraid!!
Regards, Ian.