Milling with a vertical slide on a chester conquest

[DismalduncParticipant @dismaldunc]

Hi Folks, Am just about to try this for the first time but having mucked about on a bit of scrap have some questions…

 

1, the vert slide is mounted on the cross slide, assuming I use the half nut to lock the carriage how do I advance the work in to the tool? Do I just take a spanner to the end of the lead screw and turn it ? 

 

2, I have about 0.5mm slop when the halfnut is engaged, how the devil do I improve on this?

 

3, any suggestions of the top ten things to do / not do when milling would be great!!

 

Many thanks in advance

Duncan 

[DismalduncParticipant @dismaldunc]

[JasonBModerator @jasonb]

1. If you are going to be using it a lot then making some form of handwheel will be better than a spanner but using the lead screw is the best way to do it

 

2.You probably won’t. Get a dial gauge and use this to give an accurate reading of how far you are advancing the work. It may be worth cleaning the halfnuts as they do tend to get swarf packed into them which stops full engagement and increases backlash in the screw/nut.

 

Jason

[DismalduncParticipant @dismaldunc]

Thanks Jason, I was already toying with the idea of a handwheel. I never thought of a gummed up halfnut I  will drop the apron off tomorrow and give them a clean

[Sub MandrelParticipant @submandrel]

In one halfnut is a long, thin screw that stops them engaging completely. This is deliberate as it makes screw cutting more repeatable if there is a risk of swarf on the leadscrew.

 

You can adjust this screw (and the halfnut gibs) to reduce the backlash.

 

Interestingly adding such a halfnut screw was a mod that Martin Cleeve suggested for the less well-equiped Myford

 

Neil

[Steve GarnettParticipant @stevegarnett62550]

Posted by Duncan Jennings on 23/11/2010 19:03:44:

3, any suggestions of the top ten things to do / not do when milling would be great!!

 

I think that one of the things high up in the top ten not to do list  is to attempt climb milling on a lathe; it’s going to make your lathe shudder and snatch like there’s no tomorrow…

[John OlsenParticipant @johnolsen79199]

If Duncan is trying milling for the first time maybe we should explain what climb milling is…

 

Assuming an end mill or slot drill is in use, when you are cutting with the side of the cutter, make sure that the travel is such that the job is moving towards the cutting edge. This means that the movement of the cutting edge is in the opposite direction to the movement of the job.

 

If the job and cutter are going in the same direction, it is called climb milling because the cutting edge will start its cut on the top of the job, and tend to make the cutter try to climb onto the job. It will also tend to move the job forward if there is any backlash available as there usually is. This can make the cutter try to bite off more than it can chew.

 

If you are milling a slot, one side or the other will always be climb milling, this is unavoidable. However, the other side of the slot will tend to prevent the sort of cutter deflection that causes problems. With light setups like milling in a lathe, you may find that a slot cuts happier if you always cut in the same direction. You should also make sure that any unneeded slides are locked. You will tend to find that light milling setups cut slots wider than the cutter by varying amounts. The more rigid the machine the less this tends to happen.

 

regards

John

[Steve GarnettParticipant @stevegarnett62550]

Yeah, I was going to post a link about climb milling, but I got unavoidably distracted for a while! Although, if you Google the term you get good results with pictures so I didn’t think that it was going to be too much of a problem. As far as backlash is concerned, I think it’s also worth mentioning that whilst in general this is the real killer on a lathe, the general construction of lathe cross-slides is significantly less robust than the bed of a mill as well, and this will inevitably contribute to the problem.

 

The other thing that occurred to me about this is that it’s all very well to advance the tool by rotating the leadscrew, but I think that before I was taking a cut after advancing it this way, I’d want to find at the very minimum a way of locking the saddle somehow (as mentioned by John), in the face of 0.5mm of backlash. Otherwise that really is going to add to the juddering, etc problems somewhat. This will have the same relative effect as locking the quill in position on a small mill/drill before taking a cut – almost essential on most of them!

I think that from my limited experience of doing this, I’d say that it’s clearly possible to achieve more than one might think by milling on a lathe, especially on a smaller scale, but ultimately it’s a lot more flexible on a dedicated milling machine whatever you do. Tine to start saving for one, I’d say!

Edited By Steve Garnett on 25/11/2010 23:54:14

[DismalduncParticipant @dismaldunc]

Great stuff, Thanks again for the advice, So it sounds like using a router in wood, present the work to the cutting edge of the mill . I think before I try this again I need to

1, Make some kind of carriage lock

2,check out my half nuts ( sounds a bit rude)

3, start the “Dunc need a new toy” fund and buy a dedicated milling machinev

[Gordon WParticipant @gordonw]

I am far from experienced in lathe milling but will add two , probably obvious, points. Check there is enough movement on cross slide to complete the cut.( been there).  Tighten all gibs in the absence of good locks, even if only temporary. I’m assuming a light, hobby lathe.

[Richard ParsonsParticipant @richardparsons61721]

 

I do not know the Chester Conquest, but here are a few ideas which may help. I used to mill and fly cut in the Myford using the Vertical slide, but it was not easy as you had to take it slowly using fine cuts.

Backlash – this is not always due to ware, swaff or other crud. Check, as others have suggested, the movement of the lead screw against its bearings. If there are no ball or needle thrust bearings try to fit them. Try to fit positives locks which should be independent of the gibs. The Myford cross slide has two as does my vertical slide. 

If the half nuts are worn and are not made of Mazak/pot metal they can be re-metalled quite successfully.  This can be done with the right grade of ‘Hoyt Metal’. The half nuts are cleaned up and tinned. They are then clamped together round the lead screw which has been well ‘smoked’ first. I always used to use ‘Plumbers Dirt as a mould. Hot Hoyt metal is poured in and allowed to cool.  the half nuts are cleaned and split and Bobs your fathers/mothers brother. These used to last 18 months to 2 years before the process was repeated.  

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