hollow chisel bit not fitting well

[mr_skittle]

I do the machine repair at a public woodshop and I run my own shop too. I would say that 5 thousandths of an inch on that is pretty insignificant. I doubt it would cause a big issue over the inch to inch and a length of the chisel goes through the mortiser collar. I would start by replacing the set screw, the tips of set screws can become damaged and cause a lot of issues. I've replaced several on pulleys and collars that solved problems. Does your delta have a removable collar insert, some machines do to allow different size chisels in them. You may find the rocking is from wear beyond the chisel and insert. it could be in the collar to machine connection. Since you say that you are applying a lot of pressure to get the bit through, try extending the drill bit out a tad further than on smaller bits, a 5/8 inch hole creates a bit more chips. Check for gib adjustment if the head moves at all, check for movement with someone else applying pressure. Often times I have to look beyond the initial problem to find the culprit. Did you compare the size of the LV chisels to other chisels you have? I have a set of Lee Valley premium chisels and they work well. I hope this helps. 

Paul 
Bel Air, MD

Thanks so much for all your ideas. I've exhausted most of the ideas you've brought up. I think the fact is that a 5/8 bit going through cherry is beyond the capabilities of my machine. It'll do 1/4 and 3/8 mortises all day but much larger than that and it gets iffy. I've moved on to a new idea of routing the hole out with a small bit and then rounding the corners of the tenon.

[mr_skittle]

OK, I googled it and the word can be a derogatory term loosely meaning she him. 

What are we supposed to call the thin material we have been using in machine shops and in construction to adjust things for much more than a hundred years?  

Is this what is referred to as cancel culture?

This is not an example of cancel culture. I would say it's more like political correctness. I had put c o c k - eyed in a post describing what the bit was doing and it, unsurprisingly, blocked out the first word. Because this is the "internet" I will leave it at that and not offer any sort of opinion, and thank others for refraining as well. Off-topic is a good place to discuss these issues.