Hold downs for milling slipjoint liners?

J

Jason Fry

Joined
Jun 5, 2008
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I like to mill both liners at the same time, so that I can make sure that the mill relief is lined up exactly. I'm having a heck of a time figuring out a hold down methodology that will work. Cutters keep pulling the thin liner material up and in.

Similar problem on integral bolsters. I want to mill the bolster faces in the same pass to ensure alignment, but haven't had any luck figuring out a suitable hold down.

Can y'all share some pics of your setups?

My milling experience comes only from trial and error milling knife stuff for the last 9 years. Is there an actual "right" way I just haven't learned yet?
 
I'm ignorant to the process, but I'm curious. Workholding is a fun challenge.

Do you have a pic of what you're currently doing?
 
That's a tough one indeed. I'd be tempted to mill to depth over the hole, then use the hole to secure the thin section of the liner while you mill the remainder. Requires fixture mods and small hardware, but that's what fixtures are for, eh? Alternatively you may be able to clamp in your milled area rather than using hardware.

Aside from that, general 'best practice' may work well enough. Small cutters with light cuts. Clamp as close to your work area as possible. Make sure your clamps are engaging the top face rather than the edge as to not induce a compressive load that would encourage buckling.

I've seen guys use double sided tape to help as well. Never used it myself so I can't speak to the effectiveness, but it may be worth a shot.
 
Smaller cutter may be the difference. I've been using 1/2" carbide as recommended by one of the slipjoint guys who probably has a purpose-made fixture. Name rhymes with Danely Muzek lol.

Yeah, I've tried to make sure I'm clamping on top. Tried a drop of superglue one time.
 
I'm a fan of larger cutters as well - less tool deflection and such. You may still be able to get away with it if you sneak up on your final thickness with light depths of cut.

This clamp is what caught my eye. If it's pushing on the top edge, there's a horizontal force component that's trying to buckle your liner.

hp0Qz8u.jpeg


Stack a block on your mill table to support the backside of that clamp if you're able. That'll ensure the clamp load is at the working end (clearance at the workpiece edge) and holding straight down.

Stole this pic from the internet for a visual:

215-clamping-with-stepped-block.jpg


My apologies if this is well understood. Just covering all of the bases.
 
Down cut endmills might be the answer. Also when I need to hold thin parts or need access to the entire profile of the part I use the blue tape and CA glue method.
 
A smaller end mill will be the easiest fix here. I would try a 1/4 inch. Tool deflection isn’t the issue in this case rather it’s part deflection. So the less engagement on the bottom of the tool the better.

The lower the helix of the cutter the less it will pull up as well.

Other than that better clamps as stated above will do more for you but you may need to make your own special clamps that engage as much of the liners as possible while pushing straight down.
 
clamps and thin ca glue
 

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