|LaymarCrafts Woodturning||Hints & Tips|
|Abrasive Systems for Hollow Forms and Vessels.|
In a previous article I described a series of Aids allowing me to Sand finish the inside of Hollow Forms and Pots, although these simple items have served me well I have over the last few months expanded my turning of Hollow Forms and found I needed a more efficient method of Sanding .
I was at an event where I saw a Carver using all manner of "Flapper Wheels" to finish his work and this set me thinking on ways and means of adopting such an idea for use with my hollowing requirements.
A quick troll of the Internet found that there were such items out there but as these were quite expensive, especially if I was to cover all my perceived needs, and many of these were not necessarily Flexible enough for entering into a Hollow Form or were limited in Size, my first designs were a variation of the Commercial Wheels that were available and have expanded into more efficient and flexible designs.
The Wheels that I have seen, include the Metalworkers Flapper Wheels which are very stiff and not easy to adapt for Wood, Star Wheels and Sanding Mops which are basically strips of Abrasive on a Mandrel and Radial Bristle Discs which are high tech Abrasive Wheels favoured by Woodcarvers for intricate detail Sanding.
you will require to produce these Sanding Aids is shown in the picture right.
Screws I have used 50 mm x M6 Cross Dowel Screws [2" x ¼"] or you could use Roofing Screws, the type with a domed head, I chose this type of screw as a normal hexagon headed screw has the potential to score the bottom of the Vessel when sanding.
For some of the Wheels/Pads I have cut the screws to a shorter length to enable me to construct the item and for others you may require longer screws.
Nuts and oversize Washers to suit.
Strips and Off Cuts of Cloth backed Abrasives in the various Grit types you normally use.
High density Foam.
Wadding Punches can save a lot of time and effort and a pair of Punch Pliers are ideal for making the Holes for the screw.
The Wadding Punch in the picture is 2" diameter and was picked up from a second hand Tool Dealer for a few Pounds, it is used to also cut Discs for my Hook and Loop System.
You will also need some Industrial Scissors/Shears, Adhesives, I use either Superglue or 2 part Epoxy.
The first type of Flapper Wheel comprises of a series of Abrasive Strips with a central hole through which you pass a suitable screw and then clamp the assembly together with a large washer and nut.
|The size of
each strip can be any size you choose, length and width, depending on the size of opening
it requires to go through.
The ones in the picture are approximately 60 mm x 12mm [2½" x ½"] and you can have as many strips as you feel necessary, the more you use the less flexible the pad becomes, although it is very simple to add or remove strips at any time.
You can also increase the flexibility by having narrower strips or by placing a spacer between every 3rd or 4th strip, for this I use shop made leather washers, cut from an old belt, but any flexible material would be suitable, i.e. rubber.
The bolts I use are M6 x 50mm Cross Dowel Screws which are used in Flat Pack Furniture, these have a flat head, they can be cut to a shorter length when necessary.
To make the hole in the strip you can
either drill them by bunching the strips together and drill through,
from the non abrasive side or use a hand operated wadding punch.
Although in the picture I have used a shop made knurled nut I also have a number of these pads with just an oversized washer and standard nut.
I stamp either the knurled nut with a number code that corresponds to the Grit of the Abrasive, in the picture above you can just make out the number "2" for 180g Abrasive, alternatively you can use a centre punch to do a series of Dots to indicate the Grit Size.
Once these have been used a couple of times you will find it difficult to determine what the Grit Size is so marking them now is a good thing.
I have made a couple of mandrels into which these pads can be screwed, this enables me to reach into the item being sanded and also prevents the screws from getting damaged as would occur if mounting straight into a Drill Chuck.
Details of these mandrels are given later in this article.
second version of the Flapper Wheel are made from 2" Discs
,or larger, of
Abrasive with a central hole to take the screw and then cut as shown.
These are more flexible and by varying the number of Discs you can get these Wheels through relatively small openings.
I have used a 2" Wadding Punch to cut the Discs, although any size is practical and you can vary the diameter to suit your needs.
In the centre of the Disc I have a 6mm Hole and then I cut, with Scissors, a series of radial cuts towards the centre of the Disc, the more cuts the more flexible the Wheel.
I use between 6 and 8 cuts, and also incorporate a leather spacer every couple of Discs again to improve the flexibility.
To enable me to identify the Abrasives Grit Size I have stamped the washer with the corresponding code number, i.e. 1 = 120g, 2 = 180g, 3 =240g etc. etc.
The above Wheels will adequately handle the Sanding of the inside walls of Vessels, Pots and Hollow Forms but are limited when it comes to sanding the bottom of the item, for this operation I have adopted a slightly different design.
The Abrasives require to be cut into suitable lengths and widths and then Punched with a suitable hole as shown, Type "A" is for the first Flapper Wheel detailed above and the Type "B" is used for the Bottom Sanding Pads.
|For the bottom
of the Pot or Vessel I constructed a series of Pads either with
additional "Flappers" as shown or without, the three Pads in
the centre of the picture are of this type
The three "Pads" incorporate a Disc of High Density Foam whereas the others are constructed with Abrasives only.
The picture above shows a Pad with the Foam Disc insert, the Foam needs to be cut roughly round and of a diameter to suit, this with the length of the screw will determine the minimum length of the Abrasive and the distance between the holes.
You will need to experiment here to ensure you can get the Abrasive onto the screw.
I have cut a shallow recess in the Foam to accommodate the screw head then with the screw in place you place two of the Abrasive strips at right angles and thread them over the screw as shown.
This will form a Square Pad which can be if required "Rounded" off by cutting the corners off after assembly.
The version with the "Extension Flappers" are ideal for round bottom bases or the larger base as they are more flexible and follow the contours better that the version with the foam pad insert.
Simply follow the instructions above, with or without the Foam Pad, and add any number of strips folded over and locked in place.
Having now made these Wheels and Pads you will require some form of Mandrel to hold them and at the same time allow you to reach into the Vessel/Hollow Form, I have found that this needs to be reasonably sized as if too thin it will flex and bend when in use.
|This is a 150mm
[6"] Mandrel and I also have a 230mm and 360mm [9" + 14"]
version, all are made from 12mm [½"] Ø Steel with a spigot at one
end to suit the capacity of the Drill Chuck.
The other end is drilled and tapped to accommodate the size of screws you choose to use.
I have found that I have full control over the Wheels when used with these mandrels and there is no whipping or flexing of the shaft in use.
Long mandrel with sliding support handle uses two Brass Bushes, silver soldered into a steel tube ,that allows the Mandrel to freely turn.
For the long mandrel however I did find control was precarious at times so I added a support handle.
Basic details for the mandrels, all the Mandrels I have are from 12mm ø [½"] with lengths to suit your particular requirements.
With the Handle the long mandrel is controlled from the point when it enters the Vessel/Hollow Form which is always the most critical point.
An occasional spray with a Dry Lubricant is all that is needed to keep it rotating freely.
The Flapper Wheel designed for the Metalworker is a great concept but is not flexible enough for the Woodturner so I made my own which are flexible and retain the principle of the original.
type of Wheel is ideal for Sanding not only Pots and Boxes but can be used to
Sand external surfaces of Bowls and Platters etc.
|I start by
turning a Wooden Core, this can be any size, diameter and length, but
the diameter will determine the final diameter of the wheel.
Through this I drill and recess a hole to be a tight fit for the Spindle Bolt, I again used M6 Screw so that these Wheels could also be used with the Mandrels.
With the Core still on the Lathe I fit a block of High Density Foam on to it using 2 part Epoxy as the Adhesive..
Once this is set you can then turn the Foam to its finished diameter using a Spindle Gouge and finish with Abrasive.
I have found that you require at least a layer of Foam of 10mm [3/8"] thick , so if the Core piece is say 20mm Ø then the Core + Foam will be 40mm Ø.
Part off the Core so it is flush with the foam at both ends.
You now need to cut the slots that will take the Abrasive, I have found 8 slots to be ideal and I cut these on the Bandsaw down to the wood Core as illustrated in the Sketch.
I now cut Strips of Abrasive that I will fold double and glue them into the slots using Thin Superglue.
These strips need to protrude from the slot by an amount that will ensure that if bent over they will overlap the next strip.
For the example shown, which is to the dimensions given above, each strip is 60mm which means it actually protrudes by 20mm and as the distance between each of the strips is 15mm then there will be a 5mm overlap in use.
|In the first
photo of this article you would have seen blocks of the High Density
Foam that I have been using not only for items here but also to make
Pads for free hand sanding and also to renovate my old worn out 2"
rotary pad sanders used for power sanding.
This Foam I came across by chance when my son threw out his Wave Board and as I could net get it in my Car to take it down the Dump I cut it in half on the Bandsaw and the rest is History as they say.
I have found that you can easily Shape it on the Lathe with a Spindle Gouge and smooth it off with Abrasives, it can be easily Glued to most materials with either Super Glue or 2 part Epoxy and it will also readily take Self Adhesive Velcro.
I also use it as a Wiper Pad for cleaning of my Scribbles on the Chalk Board.
Occasionally I have the need to
Fine Finish certain Items in particular Pots and Boxes, for this I have adapted
not only my system based on above but also an adaptation of the Hook and Loop
Scotch Pad is a material that is developing for Woodturners and I found
I could easily attach 2" Discs, cut with my Wad Punch, to standard
or shop made Hook and Loop Pads and this allows for a finer finish on
pre polished or even post polished items.
They will attach direct to the Pad you do not require to fix any "Loop" material to the Discs.
By putting a number of Discs on a M6 Screw Mandrel as for the items above but with the addition of a large "Penny Washer" front and back, you also can make a useful Final Polish Mop for all manner of turnings.
This is a lightweight material and its life is short but still a worthwhile addition to your Sanding/Finishing/Polishing arsenal.
Power Sanding using the above ideas will not satisfy all of your requirements and free hand sanding will always remain a necessity.
|In an earlier
article I describe how I used holders for Abrasives to get into various
Vessels and Hollow Forms these have worked to a fashion but are not as
efficient as I hoped they would be, since then I have been looking at
alternatives and have finalised on this design.
The idea is to make a smaller Sanding Head with a certain amount of flexibility built in to enable sanding of curves and contours, something that was lacking in my original designs.
The item on the right is a Guide Roller from an old printer this takes the form of a medium hard rubber roller attached to a steel bar, in fact there are often more than one roller on the bar but obviously I only need the one so the others have been removed.
I have then stuck a length of Velcro Hook Material around the Pad that I have formed and I can attach to this the Abrasive of my choice as shown on the left.
The pad for the item on the left in the picture is formed in a slightly different way by using Foam Rubber Tape, normally used for insulating water pipes, which is self adhesive and again applying a final layer of Velcro Hook Material.
The Foam Tape version is more flexible than the solid Rubber one and is better suited where you have rounded contours inside the Vessel.
The Spindles, which are about 200mm [8"] long fit into a suitable Handle, in my case one turned from Mild Steel and Knurled with a hole either end into which I can slot and fix the Spindle via a Grub Screw.
This arrangement allows me to get into the Vessel/Hollow Form and sand any of the Walls either free hand with the Lathe at rest or with the Lathe Running.
I have about 10 of these each a different diameter and the degree of softness of the Rubber Pad.
My only problem now is to find a suitable means of storing all of the various Wheels, Pads and Flappers I have made which must in total be something like 40 pieces, all different shapes and sizes as well as Grit Types.
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Last update 06 January 2010
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