Drill Chatter

[kelvin2164]

I bought a new milling machine the other day. For Aussie readers it's a Hare and Forbes HM48. A machine at the upper end, size wise, of the home workshop uasage. Trouble is, it wont drill holes without very bad chatter. I have a smaller milling machine and a pedestal floor drill. Both cut cleanly with nice curly swarf coming off. The new machine bounces and chatters and spits out finely chopped metal. I've tried every drill sharpening variation I can think of, but nothing helps. I dont want to blame the machine, it cost me a lot of money.

 

[Cogsy]

I have a HM45 which I suspect is a little smaller than yours but probably a similar design. On mine, the quill has a rack cut into it directly and the down feed (or fine feed) uses a gear meshed with the rack to lower/raise the quill. In this setup there is a lot of backlash (up to 2mm). When the quill is being lowered it's weight allows it to drop but it sits on the 'bottom' of the rack teeth. When it encounters resistance, like a plunge cut or drilling, it is free to move (or bounce) up because of the backlash in the rack. If I keep driving the cutter down I eventually overcome the backlash and can control the cutter again. The bigger problem doing it this way though, once I hit my depth and stop feeding the quill, it can still descend the amount of the backlash and go too deep.

Long story I know, but this might be your issue. If it is, I've heard it can be fixed by adding some sort of resistance (spring, shock absorber, etc) which holds the quill up against the top of the rack teeth and eliminates the backlash problem. One day I'll mod mine.

Edit to add: To test if this might be your issue, lower the quill some, then grab hold of it and see if you can lift it up at all. Even if it only moves a little it could be the cause. Another way would be to start drilling and feed aggressively and see if the chatter goes away as you force the drill deeper (using up all the backlash).

 

[Blogwitch]

The quill problem dates back to the very early Rong Fu machines and all machines that uses that system still suffers from it.

What needs to be done is to put an upwards pressure on the quill all the time it is in operation otherwise you will get this 'bouncing' or the quill dropping when machining.

When I had my RF machine, I used a strong compression spring on the depth stop, but that had limitations because I couldn't get full downwards stroke on the quill, but it did solve the problem.

I saw a much better fix a few years ago, and this C-o-C shows the basics.

At the rear of the quill by looking under, you should notice a hole in the main casting. A strong and long tension spring is attached to the back of the quill and fixed up inside the head casting. The fix I saw, the chap had drilled right thru the main head and had a long bolt that went in from one side and came out the other. The spring was suspended off the bolt and the other end of the spring attached onto the back of the quill by means of a hook drilled and tapped into the quill.
You just need to make sure that there is enough tension to hold the quill up when the quill is fully up and there is enough stretch in the spring to allow the quill go to full depth.

Hope this helps


John

 

[ROB 123]

When I use one of my tapping heads that weighs quite a lot I fasten a bungee cord around the mill head and quill it give's more upward pressure.
Its one of those that has a hook at either end, its simple to fit and adjust I just tie a knot in it if more tension is needed .
Rob.

 

[kelvin2164]

Thanks for the replies.
My other mill is an HM32 and I did exactly the modification that Blogwitch described, but not for chatter reasons, more so I could get a controlled descent with the fine feed when milling. My new machine has a big enclosed geared head (still with the same style quill feed) and would require more thought.
However I've tried a very heavy pressure on the feed in an attempt to keep the drill in contact all the time and overcome the play in the quill, but same result. Lots of banging, chattering and slivers of metal.

 

[purpleknif]

I have an XJ9512 And while I didn't have chatter problems I wasn't all that happy with the head slop caused by the rack. I put a simple counterweight on mine . Just a pulley and a length of rope with a hunk of heavy scrap . Boring mills all have a counterweight so why not mine ? Worked out great.

 

[Philipintexas]

The way I get around that problem is to tighten the quill lock-ring enough that I have to put a good bit of pressure on the down-feed. This prevents the quill from bouncing.

 

[grapegro]

Hello Kelvin, I recently bought an Optimum BF 16v mill from Hare and Forbes, and find I have made a very good choice. No drill chatter and a very tight machine. Have fitted a DRO system to it, but would like to get some knowledge about a better method of raising and lowering the "Z" axis.
Norm