Thread: Vicmarc chuck questions.

Originally Posted by ul bodger

Decidchuto lash out on the Timberbits Vicmarc chuck special and have just taken delivery of a vm100 and vm120 chuck, with the hopeful intent of going from "old school' friction chucking for bowls to the new school 4 jaw self centering set up.
Having such polished and seemingly well made chucks in the workshop is pleasing but also a bit unsettling, as I've never used these fancy things.
So if any of you fellow turners have experience with the above chucks I would really like to ask a few questions about them.
Firstly, what is that face plate ring that comes with the chuck used for? and how is it used?
Secondly, I prefer a foot on a bowl rather than a recess. No problems turning the outside of a bowl here. However when holding the foot of the bowl with the jaws on these chucks, is it inevitable that your going to get indentations where the jaws clamp on to the bowl foot?
Browsing through the instruction booklet for the chucks it also says you can use them for holding square section timber! Wondering how one might do that?
Any info appreciated.

Hi AB,
Well done on getting the vicmarc chuck, you will
not regret it,
Firstly, the faceplate ring is very usefull to screw
on to a blank and then attach them to the chuck
turn the bottom of the bowl with tennon and then
reverse , hold the tennon with the jaws, second question
I always wrap double sided tape around the foot to protect
from any marks,,,,, third question,,,, open the jaws fully and
you put a square section of timber in.....say between centres
Hope this helps and I am sure there will be other suggestions
Thats just my way of doing things!!!!!,

Look up Glenn Lucas he has some very good & useful bowl turning techniques clips on Youtube. Or sites like Brian Clifford's

http://www.youtube.com/user/GlennLucasWoodTurner

Or sites like Brian Clifford's
http://www.turningtools.co.uk/wtintro/wtintro.html

or visit you library for Mike Darlow's or Keith Rowley's books on wood turning.

South Auckland Wood Turners Guild also have some very good techniques tip sheets http://www.sawg.org.nz/tipsnjigs/

These might also help

http://vimeo.com/68649135



http://vimeo.com/68649130


http://vimeo.com/69018287

When making the tenon on the base of your bowl only open the jaws 5-6mm and you will get the optimum grip on the base. This will eliminate any marks.

Reshape a skew chisel to a 10 degree angle to match the Vicmarc jaws. This way when you create the tenon the jaws will evenly shape into the tenon.

Only make the tenon approx 3/4 the depth of the jaws so that the base of the bowl sits on the face of the jaws.

With the tenon shaped and sized properly will eliminate the need to overtighten and crush the foot, yes it needs to be tight bit not overtightened.

Another option is to glue a waste block onto the main peice and create the tenon on this peice, eliminating any markings.

Originally Posted by Jim Carroll

When making the tenon on the base of your bowl only open the jaws 5-6mm and you will get the optimum grip on the base. This will eliminate any marks.

Reshape a skew chisel to a 10 degree angle to match the Vicmarc jaws. This way when you create the tenon the jaws will evenly shape into the tenon.

Only make the tenon approx 3/4 the depth of the jaws so that the base of the bowl sits on the face of the jaws.

With the tenon shaped and sized properly will eliminate the need to overtighten and crush the foot, yes it needs to be tight bit not overtightened.
.

Thanks Jim, that sounds like pretty good advice. I was wondering how one might go about it with the jaws open really wide but I can see that's where the indents will reign supreme. Looks like I am going to have to lash out on various different jaws as well. Cripes there were a lot of variations in the instruction booklet! This looks like it might get a bit pricey.
Anyone got a boxfull going cheap?

Originally Posted by artful bodger

Thanks Jim, that sounds like pretty good advice. I was wondering how one might go about it with the jaws open really wide but I can see that's where the indents will reign supreme. Looks like I am going to have to lash out on various different jaws as well. Cripes there were a lot of variations in the instruction booklet! This looks like it might get a bit pricey.
Anyone got a boxfull going cheap?

They are not designed to be used fully open as this will gaurentee a flying missile.

You would be minimising the grip and a slight catch will ensure a ufo.

You only need to buy a couple of extra jaws as you can generally set up a foot to fit most bowl sizes.

Make sure when ordering the jaws you indicate the chuck you are using as the jaws between the VM100 and VM120 are not compatable.

Have a look here for the options

Originally Posted by Jim Carroll

They are not designed to be used fully open as this will gaurentee a flying missile.

You would be minimising the grip and a slight catch will ensure a ufo.

Jim is spot on here, and very good advice. Scroll chuck jaws have a designed grip range however they are safest at minimal opening. All chuck jaws are milled as a circle then cut into quadrants - so they are a perfect circle when the jaws are open to the width of the cut (to quarter them). They grip best and do minimal marring to the work piece when opened slightly wider than that "perfect circle" diameter.

When jaws are extended fully the jaw slides do not engage the scroll with many "teeth" however one slide will always have far less support than the rest due to the nature of the scroll design. That slide and section of the scroll have higher stress loads than the other slides and is the area of the scroll that "fails" and causes the slide and jaw to fly out. Examine the shape of the geared scroll and also the "teeth" on the back of the slides in the photo below. Never, under any circumstances remove the stop pin to "get a wider grip" as this is extremely dangerous.

vm120 parts.jpg

As the jaws are opened wider than the "perfect circle" they grip more on the center of the jaws in expansion mode; and on the "corners" in contraction mode. This action reduces the contact area between the jaws and work piece. Of more interest is the fact that the full turning forces are now concentrated on those "point" areas rather than spread across the face of the jaws and matching timber.

oops_2a.jpgoops_2.jpg This tenon failed for exactly the reasons below.

Concentrated or "point" loads stress the timber which leads to compression of the wood, which leads to vibration from a loose work piece and potential catches & flying objects. As the turner regularly "firms up" the jaws "as the keep coming loose" they are actually introducing more compression and potential stress fractures in the timber grain potentially causing the timber to fail - i..e split. Again this creates potential for UFO's & each UFO has potential to injure the turner.

This link http://www.vicmarc.com/default.asp?contentID=592 gives the dimensions of the "perfect circle" and the maximum extension of the jaws. So the safest way to go is have a range of jaw sets to suit the bowl sizes you turn. Bigger bowls require larger diameter tenons (spigots) which then require a larger diameter jaw set - not opening the jaws wider!

Using and maintaining tail stock support as long as possible also assists to reduce the potential for UFO's.

AB, I am for a gap of 2-3mm between jaws for my tenons. Gives me the best holding power/minimum crush ratio. Use a skew to create a dovetail to fit your jaws. I have on a whiteboard in view of my headstock, the diameter ranges for the different jaws I use, normally a 5mm range.

You can use a 52/3mm forstner bit to create a guide for spigot size for the normal 50mm jaw. ie drill the hole into 3mm mdf/ply/plastic etc and cut the hole in half.